Allow color scheme variation

[LennyN95]

As use cases differ, different color schemes may be more appropriate to e.g., provide a higher contrast between the studied structures.

Some ideas, how to implement his into SegDB:

• Extend the segemntations.csv by additional columns, one per color scheme and provide an argument that specifies which color scheme is used during
• Allow to define dynamic SegDB-ID <-> Color mapping that can be read into SegDB to allow full control about color custimization.

The SegDB color scheme could be implemented into MHub as a global parameter, configurable on the config level.
Alternatively, we may add segdb configuration next to those for modules.