Replaced module-art.mjs with built in art mapping function

[PrototypeESBU]

The main benefit to moving to built in is that it allows you to control the order of priority between sources. This came up when I was testing a new module.

Release notes: Cores [#911] Replaced compendium art mapping with default Foundry method.

Notes Settings for compendium art mapping are now found in Settings > Core > Compendium Art

[PrototypeESBU]

I'll need someone to test the pathfinder modules for me, as I don't own them.

[Muttley]

I'll need someone to test the pathfinder modules for me, as I don't own them.

Works perfectly with the bestiary pack I have.