l^2 stickout tracking

Scope:

• Optionally use \ell^2 as a norm for stick-out checking during tree build
• Tests for stick-out check during tree build
• Stick-out tracking in the traversal
• Tests for stick-out tracking in the traversal
• Hack List 3 construction to make use of precise box bounds
• Hack List 3 construction to make use of static \ell^2 distance criteria
• Hack List 3 construction to make use of precise \ell^2 distance criteria
• Hack List 4 construction to make use of precise box bounds (not likely to be very helpful because of isotropy)
• Hack List 4 construction to make use of \ell^2 distance criteria (No need--List 4 is P2L and hence already adapted to a circular target)
• Throw an error in case of static \ell^\infty List 3 construction and '\ell^2 stickout being used (precise is OK because that uses the extents of the actual targets in the box)

Cases to cover in accuracy/efficiency tests:

• \ell^\infty stickout + static \ell^\infty List 3 (as before)
• \ell^\infty stickout + precise \ell^\infty List 3
• \ell^2 stickout + static \ell^2 List 3
• \ell^2 stickout + precise \ell^\infty List 3
• \ell^2 stickout + precise \ell^2 List 3