Cxbx-reloaded: Add "Drag and Drop" XBE-loading feature to GUI

[PatrickvL]

Fo this issue, extend the Cxbx GUI such, that an Xbe can be loaded using a Drag and Drop operatiun.
This should only be accepted when emulation is not running.
If no XBE is loaded yet, load the dropped XBE. If an XBE is already loaded, replace it with the dropped XBE.
Be carefull to use correct paths.

Some pointers that might contain valuable information on this subject:

• https://msdn.microsoft.com/en-us/library/windows/desktop/bb776406(v=vs.85).aspx
• https://msdn.microsoft.com/en-us/library/windows/desktop/bb774303(v=vs.85).aspx
• http://www.dreamincode.net/forums/topic/293568-drag-and-drop-files-demo-in-c/
• https://helgeklein.com/blog/2010/03/how-to-enable-drag-and-drop-for-an-elevated-mfc-application-on-vistawindows-7/

[ghost]

I have implemented the feature as requested in my branch and tested with my games: they all work as before. I'll submit a new PR.

[PatrickvL]

That's great! I didn't expect a PR for this so quickly!

[PatrickvL]

Implemented in 4d30506