Some modification to the torrent files context menu.

- Added support to open directories.
- Added support to open directories parent folder.
- Make sure the directory exist before opening it.
Make torrent list rows stripped.
Fix status bar visibilty option.
Get rid of 2 redundant foreach loops, and make each torrent update itself in a background thread.
Improve webseeds handling.
Add webseeds tab.
Merge remote-tracking branch 'remotes/hexf/master'
Fix a bug in the graph updater thread.
Add informative tooltip for pieces.
Make the web seeds tab only visible if the torrent have web seeds.
Merge pull request #53 from diantahoc/master

New stuffs and improvements.