Remove socket.io per default connecting to localhost

IMO you *really* shouldn't require users to change internal javascript before being able to run on non-localhost (it should just work). This PR fixes that, relating to https://github.com/alabid/flylatex/issues/29 and https://github.com/alabid/flylatex/issues/33 . Thanks to @DavidSichau for the original solution.

I left the computation of *var socketIOURI* where it was for now, even if it is not used at the moment. It might come in handy later, or someone can remove it if it won't ever be used.