Adds directional blood trails

The blood trails now follow the path the body has taken and players can
very easily make out said path.
Heavily damaged corpses will have a much thicker blood trail than
corpses with some brute damage. At the moment, trails overwrite
eachother and a placeholder icon set is used for alien heavy blood
trails.
Makes Supply Pack datums no longer garbage collect. Prevents them from making artifacts like mulebot #3. Fixes issue #137.

Moves the supply shuttle controller to the controller folder and adds its creation to the new proc of the master controller.
Also, makes the supply shuttle make supply packs on new instead process.
Merge branch 'master' of https://github.com/tgstation/-tg-station into Supplypacks
blood trails now stack

--DO NOT MERGE STILL WIP--
Makes blood trails use overlays, the overlays are contained in a holder
object. DNA is now properly added to them.

todo: redo light, xeno light and xeno heavy trails. help of spriters is
welcome.
fixes a error I made when merging.
Finalizing blood trails

Makes trail_holder a child of cleanables instead of blood (this is to
allow add_blood turf proc to spawn blood splatter on blood trails, also
other kinds of blood effects), also cleaned up the blood code a bit.

Big props to Aranclanos, Cheridan, Pewtershmitz and all other coders on
#coderbus for making this happen.
removes extra unused code
Merged the blood trails from VistaPOWA to the latest tg code
Merge pull request #1335 from KazeEspada/supplypacks

Fixes issue #137
Merge pull request #4 from tgstation/master

github why