i-sync should look for -symbolic versions of the app icons

[Charles Kerr]

Suggested by dobey. I-sync currently gets the icon just by calling g_app_info_get_icon(). To add -symbolic support, the code would need to do something like pulling the name from the GIcon result, create a new string to append the "-symbolic" to it, and create a new GThemedIcon with that new string... something like http://bugzilla-attachments.gnome.org/attachment.cgi?id=156890