Improve HIG for moving average .ui

Change-Id: I768e409629ac0cf410163b0d3941c873be0afa85
Reviewed-on: https://gerrit.libreoffice.org/10695
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
Tested-by: Tomaž Vajngerl <quikee@gmail.com>