1. Use a better icon for stats dialog.

2. Use more reliable session_status.total_download/upload for statistics
Second attempt at fixing saving settings on shutdown.
Fix previous commit.
Make sleep and shutdown functions work on systemd's logind
Merge pull request #1199 from Gelmir/stats_new

Minor improvements to stats gathering/dialog
Merge pull request #1201 from qwerty12/master

Make sleep and shutdown functions work on systemd's logind