Setting constants

[Derkades]

Suggested in this comment: #3225 (comment)

I wonder what it would be like to create some sort of Settings class which houses the get/set methods as well as constants for common settings, in a different PR of course?

Let me know what you think of this approach before I convert everything. It is fully backwards compatible with existing code. While the old Util::setSetting and Util::getSetting functions have been deprecated, I see no point in removing them. It will only break modules without a benefit.