Improved tests and added new model properties

Added avatar property to ActionInbox.Message
Added avatar property to ActionInbox.TypeViewConv.Message
Added cover property to ActionBrowse.Result
Added avatar property to ActionUserSearch.Result
Added extendedArtists property to ActionArtist.TorrentGroup
Added artists property to ActionArtist.TorrentGroup
Created TorrentGroupArtist class in ActionArtist
Added handling for UnobservedTaskException event
Created Random class
Removed RangeSelector class
Made json error checking stricter (within ValidateJsonException method)
Made integration tests less terrible
Added assembly icon