ENH: Use global ID when inserting node in tree
BUGFIX: Restrict checking to immediate neighbors

Set the HaloSimilarityMatrix entry corresponding to
ghost halos at the previous (row) and current (column)
timestep to 0 to restrict checks to immediate neighbors.
This is done to ensure that results will be invariant
(hopefully) to the number of processors used.
ENH: Linking Halos based on GlobalID

Updated code to link halos based on the global ID and added logic
to account for halos that are not local, e.g., the progenitor and
descendant lists are updated iff the halo is owned by the given
process.