Make rulergraph a pref as well

I don't see a point in treating it differently from the other graphs.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fix odd indentation

I need to fix this in the tool as well...

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Correctly parse boolean preferences

QVariant does the right thing, regardless of whether the value is stored
as int or as string - so let's just use that instead of manually checking
for integers (and failing if the values are stored as "true" and "false").

Fixes #511

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Change the profile redraw logic after preferences were changed

I we are showing a calculated ceiling, then we have to replot the profile
after a preferences change as the gradient factors could have changed
which might change a calculated ceiling.

Also use the rulergraph preference instead of checking the settings
directly.

Fixes #511

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>