Add TL discriminator for skill defaults

[rinickolous]

Some skills have different defaults depending on TL. An example of this is the Armoury skill in Basic Set, which has different defaults based on its TL.

I propose adding a NumericCriteria to the SkillDefaults object, omitted from the data if set to "any", which causes the skill default to apply only if the criteria is met.

An alternative to this would be making duplicate listings in the various libraries for skills to which this applies. However, this seems more elegant and should be simple to implement.