Fix bug showing wrong time for first messages sent.

Fix Issue #194 .

The problem was with the time of the unsent messages.
Until the connection between the 2 users is made the first messages are stored as unsent. After that, they are pulled out of the database in local time and formatted again -> wrong time.

The solution was to pull them out as UTC time. But there was another problem. All messages that were once in the unsent they had the id = -1 and the update of an unsent message was based on the id.

So I gave every message a different id (this is the purpose of the id I believe, to be different for every item) and I modify the query for the database to search after the "successfully sent" column in addition to id.