Available property methods

[timhaywood]

Currently all Path and SourceText properties extend the standard numeric property, which includes methods such as wiggle() and loopOut(), which should be undefined.

Instead, all property classes should extend a base Property that includes the common elements, such as value, name, key etc. Then numeric properties would be an extension of this base that adds the other functions.

Ideally the numeric property methods would be undefined when PropertyValueType is not a number or array, but I'm not sure how that is possible at the moment.