Added language option to Preferences

Changing translation tested and works on:

* Windows 7
* OSX 10.8
* Ubuntu 13.04

* Updated the OSX menubar to gtkbuilder
* Added language names to the Language dropdown in Preferences
Reinserted call to translate_strings in common and renamed to translate_size_units.
Remove torrent_status translations from Daemon and move to UI clients
Use non-deprecated libtorrent parameters and functions

Also added support for seed_mode