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    problems such as silent failures in `npm outdated` and `npm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')

bin/buildDebian.sh

@@ -1,44 +0,0 @@
-#!/usr/bin/env bash
-
-# IMPORTANT
-# Protect against misspelling a var and rm -rf /
-set -u
-set -e
-
-SRC=/tmp/etherpad-deb-src
-DIST=/tmp/etherpad-deb-dist
-SYSROOT=${SRC}/sysroot
-DEBIAN=${SRC}/DEBIAN
-
-rm -rf ${DIST}
-mkdir -p ${DIST}/
-
-rm -rf ${SRC}
-rsync -a bin/deb-src/ ${SRC}/
-mkdir -p ${SYSROOT}/opt/
-
-rsync --exclude '.git' -a . ${SYSROOT}/opt/etherpad/ --delete
-mkdir -p ${SYSROOT}/usr/share/doc
-cp README.md ${SYSROOT}/usr/share/doc/etherpad
-find ${SRC}/ -type d -exec chmod 0755 {} \;
-find ${SRC}/ -type f -exec chmod go-w {} \;
-chown -R root:root ${SRC}/
-
-let SIZE=$(du -s ${SYSROOT} | sed s'/\s\+.*//')+8
-pushd ${SYSROOT}/
-tar czf ${DIST}/data.tar.gz [a-z]*
-popd
-sed s"/SIZE/${SIZE}/" -i ${DEBIAN}/control
-pushd ${DEBIAN}
-tar czf ${DIST}/control.tar.gz *
-popd
-
-pushd ${DIST}/
-echo 2.0 > ./debian-binary
-
-find ${DIST}/ -type d -exec chmod 0755 {} \;
-find ${DIST}/ -type f -exec chmod go-w {} \;
-chown -R root:root ${DIST}/
-ar r ${DIST}/etherpad-1.deb debian-binary control.tar.gz data.tar.gz
-popd
-rsync -a ${DIST}/etherpad-1.deb ./