This changes the return type of at least the following functions from IO Bool to IO (Either XmppFailure ())
* sendIQ
* sendIQ'
* answerIQ
* sendMessage
* sendPresence
Stanza send functionality now directly sends the stanzas over the wire and returns appropriate notification whether the sent succeeded (as far as we can tell)
As previously mentioned, `Context' is simply a bunch of thread
management features. This patch moves the `Context' fields into
`Session', and the `Network.Xmpp.Concurrent.Channel' modules into
`Network.Xmpp.Concurrent'.