Initiate subscription request cycle just once per activity cycle

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Fix #156: set ComposeMessage activity launch mode to standard

For some reason ComposeMessage had singleTop launch mode. While this
might have something to do with a past design, it doesn't make sense
now.

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>