Revert "Break up circular import on Python 3.4"

This reverts commit e5be48fcc0.
There are other circular imports as well.

qutebrowser/misc/sessions.py

@@ -35,6 +35,7 @@ from qutebrowser.browser import tabhistory
 from qutebrowser.utils import (standarddir, objreg, qtutils, log, usertypes,
                                message)
 from qutebrowser.commands import cmdexc, cmdutils
+from qutebrowser.mainwindow import mainwindow
 from qutebrowser.config import config
 
 
@@ -312,8 +313,6 @@ class SessionManager(QObject):
             name: The name of the session to load.
             temp: If given, don't set the current session.
         """
-        # To break up partial import
-        from qutebrowser.mainwindow import mainwindow
         path = self._get_session_path(name, check_exists=True)
         try:
             with open(path, encoding='utf-8') as f: