feat: create common action base class, implement reloading

[Ethaks]

This PR includes a refactor of actions, introducing a common OuterHeavenAction class providing a common API base to be extended by specific actions. The attack action is accordingly refactored, and a reload action is added. The base class can be further enhanced to handle any future operations meant to be common across multiple action types.

It also includes changes to styles, structuring them to be a bit more generic for general chat message usage.

Additionally, the appearance of the weapons list in the inventory is changed to make use of Foundry's ubiquitous flex styling. A grid based styling would also be possible (and likely even cleaner), although the flex one usually ends up being the most module-friendly of the bunch as modules are free to individually adjust the rendered content.
If the change is deemed worthwhile, it could be expanded to the other item categories, too.