Split internal fix STORE command into fix STORE/GLOBAL and fix STORE/PERATOM

[akohlmey]

Summary

There is next to no shared code between global and per-atom storage mode of fix STORE. In addition we need if statements to discriminate which mode is in use and some of the indexing variable use was inconsistent between the two modes.
Splitting the fix into two fixes STORE/GLOBAL and STORE/PERATOM simplifies the respective implementations and maintenance. For consistency, fix STORE_LOCAL is renamed to fix STORE/LOCAL.
This also fixes a minor related issue in the bond style bpm/rotational documentation. Thanks to @hammondkd for reporting.

Author(s)

Axel Kohlmeyer, Temple U

Licensing

By submitting this pull request, I agree, that my contribution will be included in LAMMPS and redistributed under either the GNU General Public License version 2 (GPL v2) or the GNU Lesser General Public License version 2.1 (LGPL v2.1).

Backward Compatibility

This is an internal-only command and all internal uses have been updated. External code using fix STORE will need to be updated. The section of the developer information related to porting external LAMMPS code has been updated accordingly.

Post Submission Checklist

• The feature or features in this pull request is complete
• Licensing information is complete
• Corresponding author information is complete
• The source code follows the LAMMPS formatting guidelines
• Suitable new documentation files and/or updates to the existing docs are included
• The added/updated documentation is integrated and tested with the documentation build system
• The feature has been verified to work with the conventional build system
• The feature has been verified to work with the CMake based build system