BUGFIX: Fix asserts w.r.t. Global ID assingment
BUGFIX: Supply PeriodicTransform to DIY_Enqueue

Supply dummy PeriodicTransform functor to both
halo metadata exchange and halo particle ID exchange.
ENH: Use HaloNeighborExchange instead

Use the HaloNeighborExchange object which wraps the functionality
to exchange halos with neighbors.
BUGFIX: Make GlobalID assignment contiguous

Fix issue wherein the global ID assignment logic
would leave gaps between time-steps.
BUGFIX: Remove erroneous assert

Since the merger-tree is distributed, the progenitor may in fact be
coming from another process and not exist in the local tree.
ENH: Remove warning
ENH: Extend HaloNeighborExchange API

Extend API to Enqueue halos to be sent to neighboring
processes.
ENH: Optional "inclusive" parameter to HaloExcahge

Added optional parameter that indicates whether the output
vector will include both local and neighboring halos (inclusive=true)
or just the neighboring halos (inclusive=false). Default behavior is
inclusive.
BUGFIX: Clear out enqueued halos after exchange
BUGFIX: Excahnge zombies at each time-step
BUGFIX: Mark halos as Zombies if Count > 0

When constructing a halo from a HaloInfo object, mark it as
zombie iff the Count associate is greater or equal to 1.