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/test/test_cxg_adaptor.py

@@ -0,0 +1,16 @@
+import unittest
+
+from server.common.data_locator import DataLocator
+from server.data_cxg.cxg_adaptor import CxgAdaptor
+from server.test import PROJECT_ROOT, app_config
+from server.test.test_datasets.fixtures import pbmc3k_colors
+
+
+class TestCxgAdaptor(unittest.TestCase):
+    def setUp(self):
+        data_locator = f"{PROJECT_ROOT}/server/test/test_datasets/pbmc3k.cxg"
+        config = app_config(data_locator)
+        self.data = CxgAdaptor(DataLocator(data_locator), config)
+
+    def test_get_colors(self):
+        self.assertEqual(self.data.get_colors(), pbmc3k_colors)