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/app/app.py

@@ -207,6 +207,13 @@ class DataVarAPI(Resource):
         return common_rest.data_var_get(request, data_adaptor)
 
 
+class ColorsAPI(Resource):
+    @cache_control(public=True, max_age=ONE_WEEK)
+    @rest_get_data_adaptor
+    def get(self, data_adaptor):
+        return common_rest.colors_get(data_adaptor)
+
+
 class DiffExpObsAPI(Resource):
     @cache_control(no_store=True)
     @rest_get_data_adaptor
@@ -235,6 +242,8 @@ def get_api_resources(bp_api):
     api.add_resource(AnnotationsObsAPI, "/annotations/obs")
     api.add_resource(AnnotationsVarAPI, "/annotations/var")
     api.add_resource(DataVarAPI, "/data/var")
+    # Display routes
+    api.add_resource(ColorsAPI, "/colors")
     # Computation routes
     api.add_resource(DiffExpObsAPI, "/diffexp/obs")
     api.add_resource(LayoutObsAPI, "/layout/obs")