Tweaked radiation damage from carried items

This PR implements the suggestions from #5271:
- Carried radioactive items don't contaminate the map square, but only irradiate the player
- Scanning self with the geiger counter also shows a separate count from carried items
- Added flags to allow for items that continuously emit radiation

The flags added are RADIOACTIVE, LEAK_DAM, LEAK_ALWAYS:
RADIOACTIVE && LEAK_DAM for items that leak radiation only when damaged
RADIOACTIVE && LEAK_ALWAYS for items that leak radiation always (nothing yet but adding uranium rocks to bottom of mines would be interesting).