Djsopnet: add management command for simple regression checking

Add a djsopnet_solution_regression_test command to manage.py to
performance very basic testing for changes to segment features or the
set of segments in the solution. To use, when the current database is
believed to be correct behavior:

    ./manage.py djsopnet_solution_regression_test --export
sopnet_regression_standard~

Then, once changes to sopnet or configuration have been made and the
solver has been run, the results can be checked for identity:

    ./manage.py djsopnet_solution_regression_test