Add PopulationSample and Meeting models and controllers
Add JSON response support for create and update errors
Require Request#*_responsible to be emails and don't require pbc_control_code anymore [story:41857771] [story:42257683]
Destroy attached ControlAssessments when a Control is destroyed; handle missing control cases in sort [story:42230245]
Revert Document validation changes; update tests to auto-fill the link field