Finish general Texture handling.

[skaupper]

By now the communication between the ImageInterface, FontInterface and GraphicsInterface is not as good as it could be.

A general texture need further properties in order to be rendered properly (or just to add flexibility).
A texture needs at least:

• a size
• a position
• a rotation angle
• a boolean flag for flipping horizontally and vertically
  (add more if reasonable. nothing library specific!)

Also think about what the ImageInterface/FontInterface should return. Are own Texture derivates needed or suffices Texture?

Node: Sizes and positions are relative to the parent (the element's renderBox in this case). The angle should be in radians.