Add customizations for CUSTOMER16 employees' realm

CUSTOMER16 wants their employee realm to:
* only use JWT logins
* have name changes be disabled (they want users' full names to be the
  their CUSTOMER16 user name).
* not show the suggestion that users download the desktop app

(imported from commit cb5f72c993ddc26132ce50165bb68c3000276de0)

zproject/backends.py

@@ -14,6 +14,8 @@ from apiclient.sample_tools import client as googleapiclient
 from oauth2client.crypt import AppIdentityError
 
 def password_auth_enabled(realm):
+    if realm.domain == 'employees.customer16.invalid':
+        return False
     for backend in django.contrib.auth.get_backends():
          if isinstance(backend, EmailAuthBackend):
              return True

zproject/local_settings.py

@@ -1,6 +1,7 @@
 # Secret Django settings for the Zulip project
 import platform
 import ConfigParser
+from base64 import b64decode
 
 config_file = ConfigParser.RawConfigParser()
 config_file.read("/etc/zulip/zulip.conf")