Make styleHints a variant map

The styleHints are not really flexible enough as a stringlist
as we want to be able to pass actual properties. Since we already
have a properties member of the style we should move all of our
internal properties to that.

Change-Id: Id7a66ade243461f54c41b9ec89144668aaf19483
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>