NearestNeighbours: Should be able to run on a non-parametrized instrument

[mantid-builder]

Original Reporter: @jzikovsky

Right now, without a Parameter map, you get a segfault when trying getNeighbours. Not all instruments need parameter maps and adding one to all instruments would cause slow-downs because of the way the parametrized component factory works.

The nearest neighbor info should maybe be saved in a separate member from the parameter map?

[mantid-builder]

This issue was originally trac ticket 2077