all node communication is secure now

nginx acts as a reverse proxy for node, makes ssl handling a lot easier
rethought ordering process

the web frontend only communicates with the node server through
socket.io:
all order info is saved in a node session
seats are synchronized through node
temporary reservations are not stored in the database!
after the final confirmation by the user node hands everything over to
rails which does the rest
everything gets pre-validated by node making user notification easier,
eventually rails only says yes or no to whatever node delivers

in this commit i only implemented a first step regarding seat
reservations, also removed some now-obsolete methods in the tickets
controller