* add one more layer of window
* using Path* API to operate path
* always use rappmgr.cab as file name when downloading db. ignore the URL
* add snapshot preview window
* show a broken-image icon when failed to load image
* add a padding between image and content, and make sure always some space is reserved for richedit
* hide the padding if snapshot window does not have a width
* some work to avoid blinking when window resizing
* add WM_PRINTCLIENT handling