[New Feature] Allow us to do manual RT

[Contribucious]

Would be cool to allow us to do manual RT.
Here via a right-click but that's not a requirement, that can be done via a supplementary icon for example. Or both.
Useful to RT + add just a remark in addition in one step for example.

See screenshot: http://i.imgur.com/yW3Z06D.png
That adds in the tweet field this:
RT @xxx: the tweet content.
Typically, we just need to add some text before like so (and then send it):
Eheh! RT @xxx: the tweet content.

TECHNICAL INFORMATION:
OS: Ubuntu 12.04.2 LTS (with Cinnamon)
Birdie version used: the r244 from the DAILY repository