[WIP] Working version of dune-peits in serial with latest Dune, PETSc and Zoltan

[RolandMacDoland]

Fixes #13 and #14
This branch contains new features:

• A Dockerfile to build a dune-peits environment image with Dune 2.6, PETSc and Zoltan. All necessary modules are installed and loaded using Spack/Environment modules and are ready to be used. The image can be found here https://hub.docker.com/r/uclrits/peits under the development tag. After pulling the image from DockerHub (docker pull uclrits/peits:development), and git cloning the PEITS repo, checking out the serial branch, a container can be run and synced using docker run -it -v $(pwd):/home/PEITS.
• A BUILD script that builds the dune-peits module against Dune.
• A summary of why dune-peits fails in parallel can be found in the dune-peits.cc at the Zoltan section.

[RolandMacDoland]

@dpshelio I'm happy to hear suggestions on how to make things better here.