feat: add support for powers (e.g. surges) and path skills

[stanavdb]

Type

• Bug fix
• Feature
• Refactor
• Other (please describe):

Description
This PR adds the necessary functionality for surge skills (including unlocking them). Surges have been modeled through the generic Power item. Powers are any (magical) ability linked to its own skill. Powers are set up so we can use them for the surges, but also allow support for other magic system (i.e. allomancy).
Beside Powers, this PR moves goals from the character data model to their own item (and includes migration). This allows us to embed rewards directly into goals, which is necessary for granting surges once the first ideal has been spoken.

Related Issue
Closes #88

Screenshots (if applicable)

Checklist:

• I have commented on my code, particularly in hard-to-understand areas.
• My changes do not introduce any new warnings or errors.
• My PR does not contain any copyrighted works that I do not have permission to use.
• I have tested my changes on Foundry VTT version: 12.331.

[MangoFVTT]

Went through all of this, nothing stands out as egregious and need to change to me. I'm sure there's improvements we'll have to make later but this good work to get us going 👍