Sprinting, Stamina and Temporary Modifiers (#1030)

Introduces:
- Temporary modifiers process and datums for that
- A new stamina and sprinting mechanic. That is in need of further development! Weee!

code/game/objects/objs.dm

@@ -25,6 +25,7 @@
 	var/list/icon_supported_species_tags //Used with icon_auto_adapt, a list of species which have differing appearances for this item
 	var/icon_species_in_hand = 0//If 1, we will use the species tag even for rendering this item in the left/right hand.
 
+	var/equip_slot = 0
 /obj/Destroy()
 	processing_objects -= src
 	nanomanager.close_uis(src)