* Add user-defined category-label colors
Fixes https://github.com/chanzuckerberg/cellxgene/issues/1152
As described in https://github.com/chanzuckerberg/cellxgene/issues/1307
* Respond to feedback from @bkmartinjr in nodejs
* Respond to feedback from @bkmartinjr in python
* Add tests to the server module
* Autoformat python, run linter
* Make colors_get error handling specific
* Respond to feedback from @bkmartinjr
* Respond to feedback from @bkmartinjr
* Fix whitespace
* Fix python lint errrors
* Update documentation
* Add --disable-user-colors option to launch and cxgtool.py
* Fix python formatting
* Rename '--disable-user-colors' to '--disable-custom-colors'
