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    problems such as silent failures in `npm outdated` and `npm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/urls_become_clickable.js

@@ -0,0 +1,76 @@
+'use strict';
+
+describe('urls', function () {
+  // Returns the first text element. Note that any change to the text element will result in the
+  // element being replaced with another object.
+  const txt = () => helper.padInner$('div').first();
+
+  before(async function () {
+    this.timeout(60000);
+    await new Promise((resolve, reject) => helper.newPad((err) => {
+      if (err != null) return reject(err);
+      resolve();
+    }));
+  });
+
+  beforeEach(async function () {
+    await helper.clearPad();
+  });
+
+  describe('entering a URL makes a link', function () {
+    for (const url of ['https://etherpad.org', 'www.etherpad.org']) {
+      it(url, async function () {
+        const url = 'https://etherpad.org';
+        await helper.edit(url);
+        await helper.waitForPromise(() => txt().find('a').length === 1, 2000);
+        const link = txt().find('a');
+        expect(link.attr('href')).to.be(url);
+        expect(link.text()).to.be(url);
+      });
+    }
+  });
+
+  describe('special characters inside URL', function () {
+    for (const char of '-:@_.,~%+/?=&#!;()$\'*') {
+      const url = `https://etherpad.org/${char}foo`;
+      it(url, async function () {
+        await helper.edit(url);
+        await helper.waitForPromise(() => txt().find('a').length === 1);
+        const link = txt().find('a');
+        expect(link.attr('href')).to.be(url);
+        expect(link.text()).to.be(url);
+      });
+    }
+  });
+
+  describe('punctuation after URL is ignored', function () {
+    for (const char of ':.,;?!)\'*]') {
+      const want = 'https://etherpad.org';
+      const input = want + char;
+      it(input, async function () {
+        await helper.edit(input);
+        await helper.waitForPromise(() => txt().find('a').length === 1);
+        const link = txt().find('a');
+        expect(link.attr('href')).to.be(want);
+        expect(link.text()).to.be(want);
+      });
+    }
+  });
+
+  // Square brackets are in the RFC3986 reserved set so they can legally appear in URIs, but they
+  // are explicitly excluded from linkification because including them is usually not desired (e.g.,
+  // it can interfere with wiki/markdown link syntax).
+  describe('square brackets are excluded from linkified URLs', function () {
+    for (const char of '[]') {
+      const want = 'https://etherpad.org/';
+      const input = `${want}${char}foo`;
+      it(input, async function () {
+        await helper.edit(input);
+        await helper.waitForPromise(() => txt().find('a').length === 1);
+        const link = txt().find('a');
+        expect(link.attr('href')).to.be(want);
+        expect(link.text()).to.be(want);
+      });
+    }
+  });
+});