Catalyst2.0-enabled LULESH

This is a fork of LULESH 2.0 that adds support for in situ processing using
Catalyst 2.0 (released with ParaView 5.9.0)

The codebase has the following changes:
* [`Makefile`](Makefile): updates to include new source files and add a new variable
  `CATALYST_ROOT` which must be set to point to the install prefix / root for
  Catalyst install tree.
* [`lulesh-init.cc`](lulesh-init.cc): updates to build a `conduit_node` for the mesh when Catalyst
  is enabled
* [`lulesh-util.cc`](lulesh-util.cc): updates to add a command line argument `-x` which can be
  used to pass Python scripts to execute to Catalyst.
* [`lulesh.cc`](lulesh.cc): call catalyst init/execute/finalize methods at appropriate
  locations in the simulation loop.
* [`script.py`](script.py): a sample ParaView-Catalyst analysis script