WIP:  Feature particles in Lammps

This PR contains a working wrapper which focuses on running LAMMPS using FILE-IO (i.e. we are using input files to control LAMMPS). 

Specifically in this PR, we are limiting **at first** the scope of how the user can use the LAMMPS wrapper.   Only some specific LAMMPS configuration will be supported at first.  Additionally, this PR adds only support for particles (i.e the lammps-related implementation of the ABCParticleContainer interface only has particles.  bonds will be added in a later PR).

This is work-in-progress.  The following is the goal of this PR:
- [ ] wrapper : basic sd-related methods for just ParticleContainer (e.g. get_particle_container, iter_particle_containers)
- [ ] wrapper:  subset of basic cm/sp/bc-related configuration
- [x] particle container (only particles)

Not included in this PR (but to be done in subsequent PRs) are:
- More advanced cm/sp/bc-related configuration
- Support of bonds in ParticleContainer
- Support of Mesh (i.e.for walls in lammps)
I would probably move the built into a separate bash script. It is good practice to keep the travis yml file lean.