app-window: Add Alt+Left shortcut

Add Alt+Left shortcut for

* CREDS
* PROPERTIES

https://bugzilla.gnome.org/show_bug.cgi?id=725062
app-window: Add forward & back shortcuts in wizard

Add Alt+Left and Alt+Right shortcuts in the wizard.

https://bugzilla.gnome.org/show_bug.cgi?id=725062