Documentation: adding missed documentation to edcref (map.color param)

Documentation: adding missed documentation to edcref (map.color param)

Summary:
There is param (of the map block in part's description) that allows user to
set a color for specified vertex/point of that part.
That param was undocumented so actually no one know that this param is exist and can be used in edj file.

Two main fixes:
- adding documentation for map.color param in edc reference.
- adding .edc source code example for seeing how map.color param works.

@fix

Reviewers: cedric, Hermet, raster, seoz

Reviewed By: cedric

CC: cedric, reutskiy.v.v
Differential Revision: https://phab.enlightenment.org/D1083