v.1.5 Add "data" handling.

Allow for configurable (default 1024) bytes of data to be sent to
directly connected clients.
Merge branch 'dev' of github.com:mozilla-services/pushgo into feature/data2

Conflicts:
	src/github.com/mozilla-services/pushgo/simplepush/handlers_test.go
	src/github.com/mozilla-services/pushgo/simplepush/worker.go
r? changes
Fixed maxDataLen default length
r?s

* Added wrappers for maxDataLen to warn or return error
* Moved TFlushReply to worker ad FlushData
Merging #135.
Add handlers config test.