Added IDisabledTrait & UpgradableTrait with upgrade levels support

 * IDisabledTrait for identifying (and filtering) disabled traits
 * UpgradeEnabledDisabledTrait provides an abstract base for enabling by upgrade and disabling by upgrade
The first one isn't really needed either.  Only two traits defined default upgrade types, and neither of those are needed.  The upgrade rules fix up any rules that use these traits without a defined type.