First attempt at multi-window support.
Fix lint
Fix basekeyparser tests.
Fix pyqtSlot error for downloads.
First attempt at adding a --window to commands.
Register prompt per window
Simplify showing of main windows.
Fix event filter when a non-Mainwindow dialog has an event.
Fix some objreg.get calls.
Some more objreg fixes for multi-window.
Check arguments against None in objreg.
Use collections.UserDict for LineConfigParser.
Fix lint
Add missing utilcmds import.
Clean up correctly when a window is closed.
Support opening multiple windows via init args.
Open about:blank if opening startpage fails.
Add win_id parameter to commands which need it.
Fix running of startup commands.
Move :later back from commands to utilcmds.