UNDERTOW-9 Initial SPDY integration

This is still a work in progress, however it is at the point where it can serve pages
 Minor code cleanup
Don't fail to load clients when SPDY NPN is not availble
Initial work on porting mod_proxy functionality based on the original C code
More work on mod_proxy
UNDERTOW-213 ClassCastException when SSL session tracking mode and AJP connector used
Don't dispatch to a worker when using async IO
Add configuration option to control if web socket endpoint callback invocations are run in a worker thread
Do a dispatch on complete if the initial request has not completed yet
Move changes to async context complete()
Stripping the header date from the semicolon-separated extensions before parsing
Changed regex-based stripping to indexOf semicolon
Filled in details in the javadoc for PathHandler.
Make advertise address configurable
UNDERTOW-214 javax.websocket.Session.getNegotiatedSubprotocol returns an empty String
Call the client endpoint configurator methods
Fix bug in JSR web socket buffer limit code
Fix issue with extensions
Remove unused class
UNDERTOW-216 Handle framed channel close more gracefully