BackgroundService: reduce the inactivity timeout to 30s
BackgroundService: reduce the inactivity timeout to 30s

gnome-characters does pretty much nothing during initialization:
its startup code is paging in the Unicode tables, so the tradeoff
is purely between disk access and memory usage.
By reducing the inactivity timeout we release memory more often
and let the kernel manage disk cache more effectively.
There should be no measurable CPU impact by this patch, because
the service should be sleeping most of the time anyway.

https://bugzilla.gnome.org/show_bug.cgi?id=745508

GNOME/gnome-characters,GNOME/gnome-characters,GNOME/gnome-characters,GNOME/gnome-characters,GNOME/gnome-characters