Feature - CefDragHandler

Implement basic CefDragHandler support, it's not a fully complete implementation.

Also note there's a number of files that have been deleted that are unrelated to this PR (they're just cleanup that I found along the way).

**Update**
Incomplete parts related to 
- GetFileContents
- GetFileNames (which I believe is a pointer to a vector, so I'm guessing it should be possible to remove a filename from the list)