Split out ImapConnection to its own class. This allows us to update ImapStore
without worrying about links between it and the connection.
Also, added a bit more safety to the classes in terms of correctly freeing
resources. Whenever the connection is closed, it now releases all resources.
Additionally, if the connection is ever put back in the pool, any response
data is released.
Change-Id: Ie3bda40d677707a0d6655f57175e58dece539e19
ebece4dbdc