Qt generates three change events when changing the KDE theme:
FontChange, StyleChange and PaletteChange. LO has two:
SettingChanged and FontChanged. And like Qt LO will inform all
widgets / windows independently. To prevent several redraws,
this patch just collects all Qt's change events and notifies LO
once a bit later via a Timer.

Change-Id: I9b45f543f13a84e39247a642a0e33c9ec008a46a
Reviewed-on: https://gerrit.libreoffice.org/72196
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>