Changes to MLIAP python

- update lammps python package to use setuptools
- refactor MLIAP classes into lammps python package

lammps.mliap package
- change TorchWrapper to use dtype and device as arguments
- turn activation of mliappy into functions (was a class)
- add a check to see if python interpreter is compatible
  with python lib calls internal to lammps

mliap_model_python_couple.pyx:
- load models ending in '.pt' or '.pth' with pytorch rather than pickle

python/setup.py

@@ -1,6 +1,6 @@
 # this only installs the LAMMPS python package
 # it assumes the LAMMPS shared library is already installed
-from distutils.core import setup
+from setuptools import setup, find_packages
 import os
 
 LAMMPS_PYTHON_DIR = os.path.dirname(os.path.realpath(__file__))
@@ -22,5 +22,5 @@ setup(
     url = "https://lammps.sandia.gov",
     description = "LAMMPS Molecular Dynamics Python package",
     license = "GPL",
-    packages=["lammps"]
+    packages=find_packages(),
 )