Add NPC Role selection

[Azurelol]

Adds another property for NPCs that I believe will greatly improve usability in scenarios where GMs wish to design plug-n-play adversaries that can easily scale up and down.

• The default role is Custom, in which case no updates are applied whenever an NPC changes level
• With any other role, an NPC's Attributes and Bonuses are updated based on their level and role. (So for example a Brute would have a higher might die from the start and keep scaling through the level breakpoints)

I believe I followed the established conventions for defining the role property onto the npc data model; as for the implementation and role table (what is used to query which attributes and bonuses are to be applied) I went for a simple approach which is entirely self contained and can be later refactored if need be.

A remaining sub-task to be done after is to restore an NPC's resources after level/role changes, but that is a minor QOL.