Implements first iteration of hint tracking:
- Tracks hints for the receiving (incoming) and sending (outgoing) worlds - resolves #70 (closed)
- Updates hint "found" status when items are received for tracked hints, and adds a reaction to the original hint message - resolves #72 (closed)
- Sends DM notification for new hints, if the world/player has it enabled - default is off, support for enabling in #75 (closed)
Greatly reduces message spam when hinting for specific items, as only one entry (per world) for an item+location pair will be shown in the hints channel.