Check in sockjs-client 0.3.4

Unfortunately, the build process really doesn't play well with bower. (It wants
a .git directory.)
Missing use strict
Reimplement EventEmitter

Because we really need more versions of that... sockjs doesn't export its
internal implementation.
Disable livereload

It doesn't work with CSP.
Switch the client over to use sockjs
Use a more DOM-style event emitter

It's more verbose, but it's also more idiomatic for something browser-side.
Disallow all plugins in CSP

SockJS doesn't use plugins. Best avoid them and any funny security policies
they may implement.