This patch toggles on / off the ruler via QSettings.
When the user clicks on the toolbar, this sets the settings to true /
false, in a way that if the user turns Subsurface on/ off, we still get
the last choosed option.
Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>