add open_browser trait to ExtensionApp

Author: Zsailer

jupyter_server/extension/application.py

@@ -161,6 +161,11 @@ def static_url_prefix(self):
         help=_("The default URL to redirect to from `/`")
     )
 
+    open_browser = Bool(
+        True,
+        help=_("Should the extension open a browser window?")
+    )
+
     custom_display_url = Unicode(u'', config=True,
         help=_("""Override URL shown to users.
 
@@ -319,7 +324,7 @@ def start(self):
         # Override the server's display url to show extension's display URL.
         self.serverapp.custom_display_url = self.custom_display_url
         # Override the server's default option and open a broswer window.
-        self.serverapp.open_browser = True
+        self.serverapp.open_browser = self.open_browser
         # Hijack the server's browser-open file to land on
         # the extensions home page.
         self.serverapp._write_browser_open_file = self._write_browser_open_file