Upgradeable traits are notified whenever an upgrade of their declared types are granted or revoked. The traits maintain their own internal level counter, which is then used to enable or disable the trait functionality. A trait can register for multiple upgrade types which then all affect the internal level counter.
IDisabledTrait for identifying (and filtering) disabled traits
UpgradableTrait provides an abstract base for traits to support upgrade levels
Added IDisabledTrait support to GlobalButtonOrderGenerator
Includes rework by pchote with alterations.
We split the caching SpriteLoader into a SpriteCache and FrameCache. SpriteLoader instead becomes a holder for static loading methods.
Only a few classes loaded sprite frames, and they all use it with a transient cache. By moving this method into a new class, we can lose the now redundant frame cache, saving on memory significantly since the frame data array can be reclaimed by the GC. This saves ~58 MiB on frames and ~4 MiB on the caching dictionary in simple tests.
