Bug #702709 - Do not forget to set CamelSession offline

There was missing a call to set CamelSession offline, which made
the other CamelService-s think they can do network operations,
while it wasn't true.
Bug #645476 - Avoid scroll to cursor on folder change in message list

Another take, this time, hopefully, the final. The call to e_tree_set_cursor()
also resets the view to the selected row, which we want to avoid, thus do
not do this call, if the view was regenerated on a folder-changed signal.