The GUI started to look better

Finished several small tasks:

- added color property on the property table. The color info is stored at the data level,
- improved the code that builds the grid, more property grid improvements will be made during next tasks,
- fixed some error at the Sketcher rectangle error,
- studied OCAF: used the TDataStd_IntegerArray attribute to store the RGB color info in the data tree. Found more useful attributes: the TDataStd_Current attribute at the root Label will be used to make some speed improvements, the current selected object/Label will be stored there, the TDataStd_Shape will be used to store some reference to the active shape - another speed improvement, TDataStd_TreeNode - will be studied further, building a custom Label hierarchy might help doing some speed improvements.

Will continue with adding a Name property on each Label so that each Label describes itself. In this way it can be specified what represents. Ex: a value might describe itself as being Radius, Length or Vertex.