Water example with LAMMPS

[mattwthompson]

Like #1 but with LAMMPS instead of GROMACS. Nearly all of the system setup should be doable with the same code, just swapping out writers.

This may depend on mosdef-hub/gmso#361, as @rmatsum836 noted that the LAMMPS writer may not write angles correctly (specifically, the order of atom indices in each angle).

I am going to tag a few people I know are familiar with LAMMPS who should be able to help: @shivrajkotkar @jingxiangguo @zijiewu3