Fixes #2396 and #2395: Clown's banana is regular sized and banana peels scale based on banana size

- Banana peels are now grown weapons and scale based on the size of the banana they came from
- Banana peel slip duration is now based on their potency
- Clown spawns with a 50 potency banana, which is both regular sized and
produces a skin that's nice and slippery~
- Fixes nettle and deathnettle inhands not disappearing upon use
- Makes nettle and deathnettles use the hitsound variable instead of the
playsound proc directly. Now their hitsounds will scale in volume based
on damage done.
- Makes the banana mortar shoot potency 65 banana peels. Because
otherwise it'd shoot laughably tiny and short in slip time potency
-1 ones.
- Moves corncobs to be grown weapons and updates their paths. Now their
size will scale based on the size of the corn that spawned them.
- Updates banan paths :)

Thanks Aran and Kaze for help with the changes in clown_items.dm