BitComet 0.84

- GUI Improved: new task piece graph for both BT and HTTP, displaying detail file piece downloading state
- GUI Improved: enhanced video codec version detection for preview. the extra video codec check wizard is removed.
- GUI Improved: add clipboard monitor, which can be enabled in floating window context menu
- GUI Bugfix: fix the bug that fail to open torrent file during preview
- GUI Bugfix: fix the bug that the UPNP operation results are not displayed in statistics view
- GUI Bugfix: fix the bug that the floating window is not hide when hit boss key
- Core Bugfix: fix the bug that the uploading rate is too low in some situation
- Core Bugfix: fix the bug in the decode of GZIP data returned from HTTP server