feat($goChannel): adding GoInstant channel service

The channel service follows GoInstant channel conventions, with
a couple of exceptions:

-  Creating a channel will automatically join the room specified
(defaults to lobby)
-  Messages will not be published until a connection hsa been est.
-  Methods are prefixed with $
-  $equals expects a GoAngular wrapped channel, not a GoInstant chan
test($goChannel): add test cases