[interfacekit] BScreen (again)

I'm going to post the implementation of BScreen (it's fairly simple, you will 
see) together with 
the header of BPrivateScreen (taken from libbe's dump). I researched a bit how 
BPrivateScreen works, and I also was able to use a partial implementation to 
set and retrieve the desktop colors under R5.
Since BPrivateScreen is ... well, private :), we aren't bound to a particular 
implementation, and we are free to implement it how we like. The "local" calls, 
like IndexForColor(), ColorForIndex(), etc. are already implemented (but will 
not be committed yet).

If you are interested to know how BScreen/BPrivateScreen work, I can post a 
short explanation.

Other related posts: