[ANALYZER-2336] - Update rules for applying custom series colors in CCC

* Cleaning up the way that the sunburst recognizing fixed colors.
   Instead of returning a property `isFixedColor` in the color objects (that because of that cannot be protovis cached instances), a _nully_ value is returned whenever the color is not fixed.
   In practice, not fixed colors would always be discarded, and a new color derived from the color of the parent.
* This commit should be accepted at approximately the same time as the corresponding "common-ui" commit, to avoid inconsistent builds (https://github.com/pentaho/pentaho-platform-plugin-common-ui/pull/229).