use cheerio instead of jsdom
so yeah, prolly can do this anyway?
mheh no browser requirement at all
really recreate socketio-client in expressCreateServer, fixes #2342

When using plugins, the express server gets restarted. When we do that,
the socketio-server should also get restarted. It doesn't. That means
that all the events in SocketIORouter.js are bound twice, which causes
chaos all over etherpad.

This changes our socketio.js so it fully recreates the io-instance when
we restart the server.

introduced in 95e7b0f15609fc850b71717a672abd02237a0f33, but catching
that would have been hard.
Merge pull request #2342 from ether/fix-2320-crash

fix #2320
multiline
remove jsdom dep
Merge branch 'develop' of github.com:ether/etherpad-lite into jsdom-go-away
make additional line break at end of imported doc
Merge pull request #2341 from ether/jsdom-go-away

Use cheerio instead of jsdom
Merge branch 'develop' of github.com:ether/etherpad-lite into backend-tests
handle auth fails