Consider providing API for weapon masteries to add an activity

[JPMeehan]

As a user, I would like to be able to use weapon masteries without setting up an activity to represent the mastery

Proposal: Add a new property to CONFIG.DND5E.weaponMasteries, maybe named activity, that provides activity data that is added to mastered weapons during data preparation. The actual implementation of the activities could still come from the PHB module (at least until the SRD update), but this would provide a way to implement the Cleave, Graze, and Topple masteries in a general sense.

[JPMeehan]

@arbron would appreciate labels here at a minimum

[JPMeehan]

One other thing that would be good here is effects from masteries, e.g. Sap and Slow