Fixes #2396 and #2395

- Banana peels are now grown weapons
- 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 duration 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 :)
Fixes runtime with seed extractor

Also removes unnecessary drop proc call on bluespace tomatoes, throwing
them updates the hand icon.
Merge branch 'master' of https://github.com/tgstation/-tg-station into bananfix

Conflicts:
	code/game/objects/items/weapons/clown_items.dm
Merge pull request #2657 from Tenebrosity/bananfix

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