Refactor: item threshold handling

Individual items (and groups) can have a threshold to control displayed priority based on the count received.

Consider supporting additional priority thresholds applicable to groups only:

• Comparative: an item has a certain value; when an item of that group is received with a higher value, or a lower value, show related priorities. e.g., armor or weapon groups that are not inherently progressive (or progressive items are turned off) - like ALttP swords
  • Added property per item: value
  • Added property per group: current value
• Cumulative: an item has a certain value; each item received in that group increments the total group value; set thresholds as normal to show related priorities. e.g., currency pickups that may be split across multiple distinct items - like ALttP needing ~700 rupees to cover bottle vendor, King Zora, various minigames; Rogue Legacy needing ~40k for all Manor renovation checks
  • Added property per item: value
  • Added property per group: aggregate value

Needs more thought: how multiple groups (see #52), existing threshold implementation may conflict