Add a --nowindow argument.

qutebrowser/app.py

@@ -163,6 +163,7 @@ class Application(QApplication):
         self.modeman.enter(KeyMode.normal, 'init')
 
         log.init.debug("Showing mainwindow...")
+        if not args.nowindow:
             self.mainwindow.show()
         log.init.debug("Applying python hacks...")
         self._python_hacks()

qutebrowser/qutebrowser.py

@@ -64,6 +64,8 @@ def get_argparser():
     debug.add_argument('--harfbuzz', choices=['old', 'new', 'system', 'auto'],
                        default='auto', help="HarfBuzz engine version to use. "
                        "Default: auto.")
+    debug.add_argument('--nowindow', action='store_true', help="Don't show "
+                       "the main window.")
     # For the Qt args, we use store_const with const=True rather than
     # store_true because we want the default to be None, to make
     # utils.qt:get_qt_args easier.