Mark only Sent or Received Messages

Received or sent messages are marked separately.

Addresses issue #43 (closed).

Warning: The modifications cause old databases to be unusable. Sent messages have now their type properly set to 2 in the database. Previous code contained a bug and was quite messy because message type was actually set on three places (main.qml, common.h and message_db.h). values disregarding the actual definition in message_db.h have been stored into the database! Delete all databases before running the code.