Adjust --compose Behaviour

addresses #691 (closed)

closes #691 (closed)

• Added sender='abcd' key into the --compose option:

./datovka --compose "sender='abcd',dbIDRecipient='a5s8ee1',dmAnnotation='Test message',dmPersonalDelivery='1',dmAttachment='/tmp/xsda558/request.pdf;/tmp/xsda558/explanation.pdf'"

The value 'abcd' may be the sender data-box id or username of the sender account.

• When changing the sender account in the send message dialogue window the user is asked whether we wants to retain the recipients rather than automatically deleting them.