add max_volume to furniture and use that instead of MAX_VOLUME_IN_SQUARE
add max_volume to furniture.json, mostly the default 4000, mostly
add NOITEM flag to t_hole
Extend the max_volume setting to terrain
show maximal volume for terrain7furniture and for vehicle parts in advanced inventory
use MAX_VOLUME_IN_SQUARE directly instead of using -1 as placeholder for it
Remove unused definition of MAX_VOLUME_IN_VEHICLE_STORAGE
Implemented dirty flag for map transparency cache and outside cache.
Converts most map->grid accesses to wrapper functions.

This'll make it easier to scale this up to 3d, and also to change the way submaps are stored and accessed.

Preliminary work for #6818
Fixed a few bugs with vehicle movement.
add some foldable vehicle parts & make some parts foldable
make simple wheelchair vehicle

it's non-functional as it does not have pedals, which would be silly on a wheelchair, but we don't have hand-pedals.
add generic folded vehicle item type
Use name, description, volume and weight from item::item_vars if found
Adds generic foldable vehicles.
Add hand rims, work similar to pedals

As with pedals, hand rims can not be used together with engines. Hand rims and pedals also don't work together.
remove pointless clearing of the vector

as tested the map does not contain the entry, so it's per definition already empty
Add wheel chair wheel item, wheel chair vehicle part, hand rims item

Adds recipes for them, too.
Save and load has_hand_rims status
Merge branch 'map3d_grid_access_refactor' into map3d_wip

Conflicts:
	src/map.cpp
	src/map.h