Resync he.po file
Handle reconnects inside of ImapEngine.GenericFolder

For historical reasons, reestablishing connections when a folder's
session died was handled inside of ConversationMonitor.  This broke
at some point and Geary failed to reconnect when the session dropped.

This patch puts this logic into ImapEngine.GenericFolder, where it
belongs, as well as fixes a problem in ClientSession that caused
issues when the session was closed by the server (via a BYE response).

This patch fixes bug #713609 and bug #714532.  I also believe this
fixes bug #713078.  Additionally, with the reconnect logic now in
GenericFolder, bug #714671 is solved.