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    problems such as silent failures in `npm outdated` and `npm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/bin/fastRun.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+#
+# Run Etherpad directly, assuming all the dependencies are already installed.
+#
+# Useful for developers, or users that know what they are doing. If you just
+# upgraded Etherpad version, installed a new dependency, or are simply unsure
+# of what to do, please execute bin/installDeps.sh once before running this
+# script.
+
+set -eu
+
+# source: https://stackoverflow.com/questions/59895/how-to-get-the-source-directory-of-a-bash-script-from-within-the-script-itself#246128
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null && pwd )"
+
+# Source constants and useful functions
+. ${DIR}/../bin/functions.sh
+
+echo "Running directly, without checking/installing dependencies"
+
+# move to the base Etherpad directory. This will be necessary until Etherpad
+# learns to run from arbitrary CWDs.
+cd "${DIR}/.."
+
+# run Etherpad main class
+node $(compute_node_args) "${DIR}/../node_modules/ep_etherpad-lite/node/server.js" "$@"