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    problems such as silent failures in `npm outdated` and `npm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

@@ -0,0 +1,43 @@
+'use strict';
+
+describe('scrolls to line', function () {
+  // create a new pad with URL hash set before each test run
+  beforeEach(function (cb) {
+    helper.newPad({
+      hash: 'L4',
+      cb,
+    });
+    this.timeout(10000);
+  });
+
+  it('Scrolls down to Line 4', async function () {
+    this.timeout(10000);
+    const chrome$ = helper.padChrome$;
+    await helper.waitForPromise(() => {
+      const topOffset = parseInt(chrome$('iframe').first('iframe')
+          .contents().find('#outerdocbody').css('top'));
+      return (topOffset >= 100);
+    });
+  });
+});
+
+describe('doesnt break on weird hash input', function () {
+  // create a new pad with URL hash set before each test run
+  beforeEach(function (cb) {
+    helper.newPad({
+      hash: '#DEEZ123123NUTS',
+      cb,
+    });
+    this.timeout(10000);
+  });
+
+  it('Does NOT change scroll', async function () {
+    this.timeout(10000);
+    const chrome$ = helper.padChrome$;
+    await helper.waitForPromise(() => {
+      const topOffset = parseInt(chrome$('iframe').first('iframe')
+          .contents().find('#outerdocbody').css('top'));
+      return (!topOffset); // no css top should be set.
+    });
+  });
+});