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    problems such as silent failures in `npm outdated` and `npm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

@@ -0,0 +1,69 @@
+'use strict';
+
+describe('Automatic pad reload on Force Reconnect message', function () {
+  let padId, $originalPadFrame;
+
+  beforeEach(function (done) {
+    padId = helper.newPad(() => {
+      // enable userdup error to have timer to force reconnect
+      const $errorMessageModal = helper.padChrome$('#connectivity .userdup');
+      $errorMessageModal.addClass('with_reconnect_timer');
+
+      // make sure there's a timeout set, otherwise automatic reconnect won't be enabled
+      helper.padChrome$.window.clientVars.automaticReconnectionTimeout = 2;
+
+      // open same pad on another iframe, to force userdup error
+      const $otherIframeWithSamePad = $(`<iframe src="/p/${padId}" style="height: 1px;"></iframe>`);
+      $originalPadFrame = $('#iframe-container iframe');
+      $otherIframeWithSamePad.insertAfter($originalPadFrame);
+
+      // wait for modal to be displayed
+      helper.waitFor(() => $errorMessageModal.is(':visible'), 50000).done(done);
+    });
+
+    this.timeout(60000);
+  });
+
+  it('displays a count down timer to automatically reconnect', function (done) {
+    const $errorMessageModal = helper.padChrome$('#connectivity .userdup');
+    const $countDownTimer = $errorMessageModal.find('.reconnecttimer');
+
+    expect($countDownTimer.is(':visible')).to.be(true);
+
+    done();
+  });
+
+  context('and user clicks on Cancel', function () {
+    beforeEach(function () {
+      const $errorMessageModal = helper.padChrome$('#connectivity .userdup');
+      $errorMessageModal.find('#cancelreconnect').click();
+    });
+
+    it('does not show Cancel button nor timer anymore', function (done) {
+      const $errorMessageModal = helper.padChrome$('#connectivity .userdup');
+      const $countDownTimer = $errorMessageModal.find('.reconnecttimer');
+      const $cancelButton = $errorMessageModal.find('#cancelreconnect');
+
+      expect($countDownTimer.is(':visible')).to.be(false);
+      expect($cancelButton.is(':visible')).to.be(false);
+
+      done();
+    });
+  });
+
+  context('and user does not click on Cancel until timer expires', function () {
+    let padWasReloaded = false;
+
+    beforeEach(function () {
+      $originalPadFrame.one('load', () => {
+        padWasReloaded = true;
+      });
+    });
+
+    it('reloads the pad', function (done) {
+      helper.waitFor(() => padWasReloaded, 5000).done(done);
+
+      this.timeout(5000);
+    });
+  });
+});