Fixed coloring. Added events when data changed.

Some issues arose when I made changes for mac compatibility. Now the app
tests for OS and changes the way it draws accordingly.
When Data values are changed in a Dimension Editor or just Dynamic Data
Display object, an even is generated, so parents can listen for when a
value changes.
Added scale and offset operations.

In both part view and printing:
The user can specify the scale of the part relative to number in the STL
file (an associated unit library was added, but is not yet accessible).
Offset values for the part are shown will quickly update in the display
view and also affect the bitmap generation.