new passphrase prompt activity
// FREEBIE
Reactivate a group if a contact gets readded

Fixes #723 //FREEBIE

Removes the own number from group on leaving, to receive a proper
re-added message
Save drafts for recipients without an existing thread
Clear drafts when deleting conversation(s)

- Also don't save drafts when the thread was deleted from the
 ConversationActivity menu

otherwise the drafts stay in the database and will reappear when a thread
with the same threadId is created