Launch browser to cellxgene (#325)

* Launch browser to cellxgene

Also added  --no-launch command line parameter

* Don't launch browser for tests

* rename no-launch to no-open

* Rejigger -no-open to positive destination

so later logic looks cleaner

server/test/test_api.py

@@ -25,7 +25,7 @@ class EndPoints(unittest.TestCase):
 
     @classmethod
     def setUpClass(cls):
-        cls.ps = Popen(["cellxgene", "scanpy", "example-dataset/"])
+        cls.ps = Popen(["cellxgene", "--no-open", "scanpy", "example-dataset/"])
         session = requests.Session()
         for i in range(90):
             try: