Makes trays a subclass of bag.
This somewhat changes how items are placed on them, but for the better as it's more consistent with existing mechanics.
Hitting someone with the tray still scatters the contents around!  Works on nonhumans.
Placing icons on the tray still makes them show up on the tray.  Using the tray on a table now places the items onto the table, or places the tray itself if it's empty.  Robots can't lose their tray this way, I checked.
Service borgs can actually use their tray to carry things!  Trays can hold all sorts of stuff, as long as it's small...
A service borg can carry the nuke disk around.  The pinpointer does follow it correctly.
If the service borg stashes its tray module, dies, explodes, gibselfs, or is forced to stash its modules by damage, it drops all the tray's contents on the ground.

Fixes #236 (service borgs can't use trays) and #2991 (Items on food trays can't be picked up).  Didn't address #1919, the layer issue.

Fixes the "bajillion lines changed" with the maps.
Over-eye hair improvements

-Long Over eye looked like two different hairstyles layered on top of each other when it was made, giving it a weird spiky look around the face area when seen from the side. I've completely redone the side sprites.
-Regular Over eye had inconsistent side sprites which made it look a lot longer than it should.
carved books now turn into storage items
forgot to include the fucking book itself
Fixes Immovable Rod

-Rod no longer gets deleted after hitting a few objects
-Rod no longer gets stuck in the rare case it hits a shuttle at just the right angle. It now explodes.
Fixed ling regeneration bugs

It now requires DNA, preventing infinite genomes, and now correctly
displays the chemical cost, rather than leaving lings thinking that 10
chemicals would be sufficient to revive.
Resolved Conflicts:
	code/modules/events/immovable_rod.dm
Merge branch 'master' of https://github.com/tgstation/-tg-station into Issue236_Trays

Conflicts:
	_maps/map_files/tgstation.2.1.2.dmm (The map was deleted)
	code/game/objects/items/weapons/kitchen.dm (Someone fixed up tray attack code a little, whereas I moved trays to a subclass of bags and made the attack code very simple by comparison.  Went with my solution.)
Merge branch 'master' of https://github.com/tgstation/-tg-station into Issue236_Trays

Conflicts:
	code/game/objects/items/weapons/kitchen.dm (Resolved, we were both removing snowflakey tray code)
Slime changelog update
Merge pull request #3712 from Ikarrus/overeyefix

Over-eye hair sprite improvements
What did I break
Dammit
Merge pull request #3766 from Kelenius/OfSlimesAndChangelogs

[CHANGELOG] Of slimes and changelogs
Merge branch 'master' of https://github.com/tgstation/-tg-station into Issue236_Trays
Merge pull request #3655 from Rolan7/Issue236_Trays

Makes trays a subclass of bag.
Merge pull request #3729 from Ikarrus/immovablerod

Fixes Immovable Rod
Merge pull request #3732 from AlexanderUlanH/baccano

Fixed ling regeneration bugs
Merge pull request #3720 from hornygranny/readingrainbow

carved books now turn into storage items