Connection check should be skipped if the user has logged out, otherwise
`app-db` may end up in an invalid state which causes an error and red screen
in dev mode.
- do not logout and remove previous mailserver
from peers when changing mailserver
- rename wnode mailserver
- move transport.inbox to mailserver.core
- fix all subs and db keys
Signed-off-by: yenda <eric@status.im>
