Precalculate viability

[nedtaylor]

Evaluate the viability of each point and store it. Then pass this map to add_atom_min, so you don't have to recalculate each point every time a new atom is added, you just update each species-dependent map. MIGHT be faster.

[nedtaylor]

Implemented. Now need to have it only calculate this for species in the placement_list (and know how to reference that).

[nedtaylor]

Implemented. Now need to have it only calculate this for species in the placement_list (and know how to reference that).

Implemented.

[nedtaylor]

Closed with merge request #10