Local event optimisation

[toastedcrumpets]

Currently, local events are not optimised using neighbour-lists. The previous implementation was not compatible with infinite systems or compression dynamics.

This can be corrected by first removing all "infinite" objects (e.g. infinite planes) and replacing them with bounded objects with a volume (walls have a thickness and finite area).

Then these objects can have bounding boxes determined for them. This bounding box interface can then be used by the neighbour list to insert Locals in to itself, and to determine when they will become invalid.

This issue is relevant to issue #2.