Created update_db_version for opening older versions of the Scenario.
Migrations should include the record of the DB as it is AT THE END of the migration, then intended state.  This was fixed.
Not relying on scenario_filename until we split databases.
Comment on Foreignkeys
Fixed field name typo
Added support for Piecewise and Histogram.  Rearranged equation_type ordering.
Added migration for previous commit
Merge remote-tracking branch 'origin/master'
Merge branch 'migrations'