Connect and disconnect from context menu

We have a list of all accounts in the server window, but there's not
much we can do with them. Add a context menu to the outline view where
we can connect or disconnect to the server.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Close connection if initialization fails

The connection is maintained if we open it successfully but fails at the
TLS handshake. Close the connection if we're unsuccessful.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>