Added bigbox basedent to test carrying items that are larger than the box. It has some kinks due to exceptions made elsewhere in the code that only consider the regular box. It doesn't inherit because due to the name, box loads first and doing a local require may have unforeseen consequences.

Added UNI_SIZE basedent static to replace GRAPHIC_OFFSET, GRAPHIC_QUADCENTER, and PHYS_SIZE for simple and derivable entities.
Added MAPPABLE_CENTERX and MAPPABLE_FLUSHY basedent statics to center an object along its X and make it flush against the ground on spawn, respectively.
Made the CanCarry basedent mixin responsible for handling userects.
Made it so that userects set their position with their parent's speed in mind so there's minimal lagging in its position.
Made it so that set* methods of HasGraphics and HasPhysics will accept a table for its first argument in place of all the other args, or clone the last received arg in place of any that are missing.
(eg: set*(12) = {x=12,y=12,z=12} or set*(12,3) = {x=12,y=3,z=3} )
Made the box derive its graphic names from the classname.
Appended legacy_shotted and legacy_stomp with some code snippets introduced by alesan99.
Added first instance of box to the convenience pointers table.