test for pass phrase cross checked + stored when sending message

[tomholub]

Have to write a test for this too:

1. start composing a message
2. it asks for pass phrase for draft
3. give it a wrong one
4. it must not be accepted, a new prompt must show
5. give it a correct one
6. it should not ask again when sending
7. I should now be able to go to the sent message and read it without re-entering pass phrase

Originally posted by @tomholub in #860 (comment)

[tomholub]

not actionable until #854 merged