restructure: move bin/ and tests/ to src/

Also add symlinks from the old `bin/` and `tests/` locations to avoid
breaking scripts and other tools.

Motivations:

  * Scripts and tests no longer have to do dubious things like:

        require('ep_etherpad-lite/node_modules/foo')

    to access packages installed as dependencies in
    `src/package.json`.

  * Plugins can access the backend test helper library in a non-hacky
    way:

        require('ep_etherpad-lite/tests/backend/common')

  * We can delete the top-level `package.json` without breaking our
    ability to lint the files in `bin/` and `tests/`.

    Deleting the top-level `package.json` has downsides: It will cause
    `npm` to print warnings whenever plugins are installed, npm will
    no longer be able to enforce a plugin's peer dependency on
    ep_etherpad-lite, and npm will keep deleting the
    `node_modules/ep_etherpad-lite` symlink that points to `../src`.

    But there are significant upsides to deleting the top-level
    `package.json`: It will drastically speed up plugin installation
    because `npm` doesn't have to recursively walk the dependencies in
    `src/package.json`. Also, deleting the top-level `package.json`
    avoids npm's horrible dependency hoisting behavior (where it moves
    stuff from `src/node_modules/` to the top-level `node_modules/`
    directory). Dependency hoisting causes numerous mysterious
    problems such as silent failures in `npm outdated` and `npm
    update`. Dependency hoisting also breaks plugins that do:

        require('ep_etherpad-lite/node_modules/foo')

src/tests/frontend/specs/chat.js

@@ -0,0 +1,116 @@
+'use strict';
+
+describe('Chat messages and UI', function () {
+  // create a new pad before each test run
+  beforeEach(function (cb) {
+    helper.newPad(cb);
+  });
+
+  it('opens chat, sends a message, makes sure it exists ' +
+      'on the page and hides chat', async function () {
+    const chatValue = 'JohnMcLear';
+
+    await helper.showChat();
+    await helper.sendChatMessage(`${chatValue}{enter}`);
+
+    expect(helper.chatTextParagraphs().length).to.be(1);
+
+    // <p data-authorid="a.qjkwNs4z0pPROphS"
+    //   class="author-a-qjkwz78zs4z122z0pz80zz82zz79zphz83z">
+    //   <b>unnamed:</b>
+    //   <span class="time author-a-qjkwz78zs4z122z0pz80zz82zz79zphz83z">12:38
+    //   </span> JohnMcLear
+    // </p>
+    const username = helper.chatTextParagraphs().children('b').text();
+    const time = helper.chatTextParagraphs().children('.time').text();
+
+    expect(helper.chatTextParagraphs().text()).to.be(`${username}${time} ${chatValue}`);
+
+    await helper.hideChat();
+  });
+
+  it("makes sure that an empty message can't be sent", async function () {
+    const chatValue = 'mluto';
+
+    await helper.showChat();
+
+    // simulate a keypress of typing enter, mluto and enter (to send 'mluto')
+    await helper.sendChatMessage(`{enter}${chatValue}{enter}`);
+
+    const chat = helper.chatTextParagraphs();
+
+    expect(chat.length).to.be(1);
+
+    // check that the received message is not the empty one
+    const username = chat.children('b').text();
+    const time = chat.children('.time').text();
+
+    expect(chat.text()).to.be(`${username}${time} ${chatValue}`);
+  });
+
+  it('makes chat stick to right side of the screen via settings, ' +
+      'remove sticky via settings, close it', async function () {
+    await helper.showSettings();
+
+    await helper.enableStickyChatviaSettings();
+    expect(helper.isChatboxShown()).to.be(true);
+    expect(helper.isChatboxSticky()).to.be(true);
+
+    await helper.disableStickyChatviaSettings();
+    expect(helper.isChatboxSticky()).to.be(false);
+    expect(helper.isChatboxShown()).to.be(true);
+
+    await helper.hideChat();
+    expect(helper.isChatboxSticky()).to.be(false);
+    expect(helper.isChatboxShown()).to.be(false);
+  });
+
+  it('makes chat stick to right side of the screen via icon on the top' +
+      ' right, remove sticky via icon, close it', async function () {
+    await helper.showChat();
+
+    await helper.enableStickyChatviaIcon();
+    expect(helper.isChatboxShown()).to.be(true);
+    expect(helper.isChatboxSticky()).to.be(true);
+
+    await helper.disableStickyChatviaIcon();
+    expect(helper.isChatboxShown()).to.be(true);
+    expect(helper.isChatboxSticky()).to.be(false);
+
+    await helper.hideChat();
+    expect(helper.isChatboxSticky()).to.be(false);
+    expect(helper.isChatboxShown()).to.be(false);
+  });
+
+  xit('Checks showChat=false URL Parameter hides chat then' +
+      ' when removed it shows chat', function (done) {
+    this.timeout(60000);
+
+    setTimeout(() => { // give it a second to save the username on the server side
+      helper.newPad({ // get a new pad, but don't clear the cookies
+        clearCookies: false,
+        params: {
+          showChat: 'false',
+        }, cb() {
+          const chrome$ = helper.padChrome$;
+          const chaticon = chrome$('#chaticon');
+          // chat should be hidden.
+          expect(chaticon.is(':visible')).to.be(false);
+
+          setTimeout(() => { // give it a second to save the username on the server side
+            helper.newPad({ // get a new pad, but don't clear the cookies
+              clearCookies: false,
+              cb() {
+                const chrome$ = helper.padChrome$;
+                const chaticon = chrome$('#chaticon');
+                // chat should be visible.
+                expect(chaticon.is(':visible')).to.be(true);
+                done();
+              },
+            });
+          }, 1000);
+        },
+      });
+    }, 1000);
+  });
+});