Refactor HEDM functionality

[joelvbernier]

We would like to create a HEDM package to house all HEDM-specific packages/modules. The most logical place for this the root level of the repo.

• [ ] Collect the ff-HEDM workflow modules
  • the config pakckage, as it is ff-HEDM specific at the moment
  • the cli package (ditto)
  • findorientations.py
  • fitgrains.py
  • hexrd.xrdutil.nf-hedm
  • hexrd.grainmap
• [ ] Generalize the config and cli packages to include nf-specific options
  • NOTE: this is trigger a new API and version number increment
• [ ] Split of tomography utils in their own subpackage.

[joelvbernier]

@darrencpagan -- we should finalize a specification for the yml block describing nf parameters.

[ZackAttack614]

We are refactoring all of hexrd at the moment. We can revisit further changes beyond version 1.0 in the future.