Implement fafnir medals

[SapiensAnatis]

Context
In the original game you could acquire fafnir medals, at 50 medals per week, as a random drop from quests. These would be used in a treasure trade shop to buy rare items.

The feature request
These medals should be implemented in Dawnshard. They can randomly drop from quests and are available from certain other treasure trades.

Additional information
The internal term for these medals is gather_item so they are sent from load/index under gather_item_list. The only gather_item_id in the master asset is 10001 which is fafnir medals (this implementation indicates that other gather items may have been planned 🤔)