isMajorPowerType
Null-safe classification of a power type into the major / minor buckets used by the power stance rings and by com.magmaguy.elitemobs.mobconstructor.EliteEntity when counting powers. Anything that isn't explicitly a MAJOR_* type counts as a minor power, which is how the counters have always behaved.
Return
Whether the power type belongs to the major power bucket
Parameters
powerType
Power type to classify, may be null