Clay And Pottery pack. Part 1.

Construction options:
1. Cut Down Grass
2. Remove Dirt Mound
3. Extract Clay Mound
Items:
1. Clay jug
2. Clay bowl
3. Clay container
4. Clay canister
5. Clay pot
6. Clay quern
7. Clay teapot
8. Clay lump
9. Brick
New materials:
1. Fresh Clay
2. Clay
New terrain object:
1. Clay mound
Remove unneeded space.
Change clay mound.
Remove flags from clay bowl.
Change clay vessels recipes.
Const accessors in preperation for more const changes.
Use auto and existing map methods to reduce reliance on i_at() returning a non-const vector.
Add i_at_mutable() for code that needs direct access to map item lists.
Add accessors to safely access items on the map.
Make map::add_item() public to bypass certain checks when necessary.
Split handling of map items and vehicle items so map items can be handled more safely.
The payoff, make map::i_at() const to reduce risk of bypassing caching.
Reorder charging station checks for slightly better performance.
Fix lua accesses of items.
Added hkey for alarm, changed hkey for door toggle
Fix brackets
Remove "remove dirt mound".

I didn't notice that you can already remove dirt mound using "tamp ground" option.
Use correct indices when deleting items run over by a vehicle.
L2037 description
Merge pull request #10354 from SpongeTheGlaive/l2037-description

New L2037 description