Minor spelling corrections; remove unused imports.
Add debug output to try and solve problems with Heroku.
Bump the required JDK version from 6 to 7.

The Undertow web server apparently requires JDK 7. Although Undertow
compiles on JDK 6, the server will crash whenever the websocket
server receives a new connection. The crash appears to be related to
ConcurrentLinkedDeque not being available on JDK version 6.

Fixes #1.