Add support for more event types

This could use [`-mtl_valueMappingTransformerWithDictionary:defaultValue:reverseDefaultValue:`](https://github.com/Mantle/Mantle/blob/f797bd4837b61d37847a4833024aab268599a681/Mantle/NSValueTransformer%2BMTLPredefinedTransformerAdditions.h#L70) instead. (That method didn't exist when the other events were implemented.)