Merge DASSH_MIA into DASSH_integration

The unit tests with reference DASSH inputs have been updated to use reference paths relative to the absolute path of the PyARC test directory; the reference inputs have placeholders that are replaced by the proper path at test execution.

Note: two of the three commits were me merging DASSH_integration into DASSH_MIA so that the branch would be up to date and could be merged back in with DASSH_integration.