Handle bad parameters, HarvestSourcesController#update

Make the update action return a Bad Request response if it gets
illegal parameters.
Add HarvestSourcesController tests

Add tests for create and update actions.
Fix rendering error with harvest source form

Parameterize form action so it works with edit or create.
Add harvest source deletion (broken)

Add #destroy action for harvest source.
It seems to work fine, but the rspec test does not work.  See
"FIXME" comment in the test.