Based on profiling, Writer's most CPU consuming idle event was
document statistics calculation.
This patch stops the idle timer once statistics has been updated.
Subsequent profiling shows a sharp decline in CPU usage.

Modifications to the document should initiate statistics update.

Change-Id: I8c38ad8847987264549945e4f482ea18d2635283
Reviewed-on: https://gerrit.libreoffice.org/14575Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>