Add user-defined category-label colors (#1402)

* 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'

server/cli/prepare.py

@@ -73,7 +73,8 @@ def prepare(
     (h5ad, loom, or a 10x directory), runs dimensionality reduction,
     computes nearest neighbors, computes an embedding, performs clustering,
     and saves the results. Includes additional options for naming annotations,
-    ensuring sparsity, and plotting results."""
+    ensuring sparsity, and plotting results.
+    """
 
     # collect slow imports here to make CLI startup more responsive
     click.echo("[cellxgene] Starting CLI...")