Finer-tuning control for the number of output tetrahedra

[jalevine]

It would also be interesting to specify target tetrahedra resolutions on a per material basis. For example, setting material 1 to always be at the finest resolution, while allowed material 2 to use larger tets.

Again, this is a matter of octree construction, but it would have to be carefully informed as to which materials are in which cells wrt different targets. The cmdline interface would also be a bit tricky to implement (you'd have to specify values per material). But, it could be a useful feature if users know they need resolution for different materials but can sacrifice it for others.

[zaracay]

Cardiac propagation models would benefit from this feature. Typically heart cells need to be very small and torso cells (which act only as volume conductors) can be larger.