createChannel updated. getChannelURL added

Now createChannel function uses more secure "transaction" method to
create the new channel rather than using "set" method. This will ensure
that a new channel will not be created if there already is a channel for
this id.

Also this function now supports 3 callback methods for success, channel
exists and failure statuses.
Fixed bug: creatChannel not functions

More:
Updated create channel test case.