Add support for feature restrictions with user feedback in compendium browser

[arbron]

When selecting a feature such as an Eldritch Invocation through the compendium browser, there should be a method for displaying whether the user qualifies for that feature and if they don't tell them why not. This could be handled by an additional callback passed through the compendium browser that is called for each index/item. This callback would return a status (approved, rejected, neutral) as well as an optional explanation (e.g. "You need the Fighting Style class feature to take this fighting style feat.").

The compendium browser could then display a checkmark or x-mark next to each item to make it clear what can be selected, invalid items can have their checkboxes disabled, and mousing over the icon can display the explanation.

Would help resolve part of #4686