GUI Improved: cleaned up and improved a lot of code, reduce program size

GUI Improved: add VIP download list button in task list toolbar

GUI Improved: do not allow hide the title column of task list

GUI Improved: new command in View menu: Find Task (Ctrl+F)

GUI Improved: switch file list to Simple List or Tree List, from context menu

GUI Improved: display the tree list of files correctly when the files in Torrent are not sorted by directories

Core Improve: support Firefox 7

Core Improve: the file size limit of Torrent changed to 10MB

Core Improve: support torrents whose piece size is not the integral multiple of 16 KB