Move all admin settings from the domain table to the settings table

A lot of the admin settings still are stored in the civicrm_domain table when they should really be moved to the civicrm_settings table (or is there a set of criteria for storing a setting in one or the other table?)

I have the feeling this migration was started but kindda left in the middle, with some settings having being migrated and not others. It might be a good thing to have this legacy fixed, and all settings stored in a consistent manner, prior to moving to 5.0.