First prototype of HSV color space based dynamic DN element coloring

First prototype of HSV color space based dynamic DN element coloring

Both VertexNode and EdgeNode support a new property 'dynamicColor' that
can be set to either a Color or null.

DN.Diagram has three new properties:
* Element Color Hue
* Element Color Saturation
* Element Color Brightness Function

where the first two are constants and the last one is a (Resource ->
<ReadGraph> Double) function that is expected to return a value in [0,1]
which is then used to get the final element color from the HSV gradient.
The Resource argument is the DN diagram element.

The function allows users to define any complex functions in SCLMain to
perform the evaluation for the DN element.

gitlab #2

Change-Id: Ia8dbe0df9400242670949da91e373d68cf7ff758