Add the option, if possible. So that the band of health of the target is slightly outscored in width, unlike the others (those who are not targeting).

This can do target scaling: https://github.com/kesava-wow/kuinameplates-customs/blob/master/custom.target-scale.lua, but it's ugly-scaling, meaning it might introduce aliasing problems.

This is an ongoing consideration, so I'll move it here: #287.