Make the CDK 2D atom colors modifiable and simplar with a map instance.

Change-Id: Ic22c6a731c56217ded2ca6e43f8df9b96ddb5d19
Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Extend CDK 2D atom coloring.

Change-Id: I7e897c9a9b35a7e972350bc6accd60b580163b8a
Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>