jamiaccount: extract conversation's related code from class

This patches introduces two new concepts in order to reduce the code
of JamiAccount.

ChannelHandlers to manages protocols logic. The idea of this class
is to handle channels per protocol, accept and reject it.
AccountModule, to be able to separate logic between call managements
datatransfer, config and conversation but give an interface to
detect when some events should occurs.

Change-Id: I34ff07852c06d7266411f1ffb32b71a1834aba4f
GitLab: #603