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    problems such as silent failures in `npm outdated` and `npm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

@@ -0,0 +1,68 @@
+/*
+ * Fuzz testing the import endpoint
+ * Usage: node fuzzImportTest.js
+ */
+const common = require('./common');
+const host = `http://${settings.ip}:${settings.port}`;
+const request = require('request');
+const froth = require('mocha-froth');
+const settings = require('../container/loadSettings').loadSettings();
+
+const apiKey = common.apiKey;
+const apiVersion = 1;
+const testPadId = `TEST_fuzz${makeid()}`;
+
+const endPoint = function (point, version) {
+  version = version || apiVersion;
+  return `/api/${version}/${point}?apikey=${apiKey}`;
+};
+
+console.log('Testing against padID', testPadId);
+console.log(`To watch the test live visit ${host}/p/${testPadId}`);
+console.log('Tests will start in 5 seconds, click the URL now!');
+
+setTimeout(() => {
+  for (let i = 1; i < 1000000; i++) { // 1M runs
+    setTimeout(() => {
+      runTest(i);
+    }, i * 100); // 100 ms
+  }
+}, 5000); // wait 5 seconds
+
+function runTest(number) {
+  request(`${host + endPoint('createPad')}&padID=${testPadId}`, (err, res, body) => {
+    const req = request.post(`${host}/p/${testPadId}/import`, (err, res, body) => {
+      if (err) {
+        throw new Error('FAILURE', err);
+      } else {
+        console.log('Success');
+      }
+    });
+
+    let fN = '/test.txt';
+    let cT = 'text/plain';
+
+    // To be more aggressive every other test we mess with Etherpad
+    // We provide a weird file name and also set a weird contentType
+    if (number % 2 == 0) {
+      fN = froth().toString();
+      cT = froth().toString();
+    }
+
+    const form = req.form();
+    form.append('file', froth().toString(), {
+      filename: fN,
+      contentType: cT,
+    });
+  });
+}
+
+function makeid() {
+  let text = '';
+  const possible = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
+
+  for (let i = 0; i < 5; i++) {
+    text += possible.charAt(Math.floor(Math.random() * possible.length));
+  }
+  return text;
+}