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
Replace deprecated session.num_connections with session_status.num_peers

This commit removes get_num_connections() from core and updates UIs
to use get_session_status with num_peers key.

Extra noise is from Flake8 changes
Put setup_translation back into start_daemon

A 3rd party plugin broke because using _() in core files so reverting
to prevent issues and may also be useful in future for translating
the help text.
Replace lt deprecated session funcs with session_settings
More removal of lt deprecated params and funcs

Due to a deprecation mistake get_settings() should be used for python
bindings and it will return a dict.
Remove stray debug logging line
Fixes for #367 : Don't store last_seen_complete and total_uploaded in state file
Fixes for #607 : Add completed_time to core and Completed column in GTK UI
Remove leftover total_uploaded state code
Fix #1000 : GTKUI: Select first row in list if no rows are selected

Also do not remove selection when changing filter (as 1.3 works)
Fix issue with add_torrent_params flags