initial implementation of red-black tree insert

Hi - here is the initial implementation of red-black tree insert, based on Introduction to algorithms.

I had to do 2 small corrections to client/containers/tree:
 - allow to insert a child without a parent (explained in code comment why this might happen)
 - changes in root setter, which did not made sense to me (setting node.parent.parent = node)

Please note, that this is an initial implementation, and I will work on making it more readable, clean, and covered with tests - but I wanted to get the code out for your review early - any suggestions are welcome.

Also - I couldn't find a way to visually color tree nodes - can you point me in the right direction?