Clipboard os specific

This is just a backup platform specific code for clipboard. This frees us from being too dependent on any one library like pygame or sdl2.

Windows: win_ctypes
Linux: dbusklipper
OSX: NSPasteboard(requires pyobjus: obligatory dog food post...)

ios: Not yet implemented
Android already had android_clipboard.

Tested to work on linux, windows and osx.
The only part left to include is the iOS clipboard implementation, that can be included later.