Move overmapbuffer::find_all to overmapbuffer
add overmapbuffer::get_npcs_near_player to get all npcs in a range, on any overmap
add vehicle with tracker to the mini map
add overmapbuffer::find_npc to find NPCs by id in any overmap
make npcs location stable and global, independent of active state
Merge continuing overmap interface cleanup, with NPC fixes.