This refactors DocumentTimerManager to export the busy status
independent of the Idle function. This way it can be ignored in
the Scheduler while the document is busy,

Change-Id: Icec2075d3338ad8dd4440678eb0570d7fe887778
Reviewed-on: https://gerrit.libreoffice.org/43197Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>