this will:
- draw lattice boundingboxes in 3dView [if "show_bounds" is used -- an option previously pretty useless for lattices]
- give proper values for lattice objects ".bound_box" in bpy
- give proper values for armature objects ".bound_box" in bpy
- lets users use "Dimensions" [in 3dView Transform panel] on lattices and armatures
- remove redundant calculations in "boundbox_armature()"
- (armatures boundingboxes were already drawn in 3dView [if "show_bounds" is used])
based on report T45735: Lattice's bounding_box doesn't update and a comment in code by @Campbell Barton (campbellbarton) "* later we may want to add dimensions for lattice, armature etc too */