Add a setting in dev and test to make mass assignment errors obvious

As recommended by
http://code.tutsplus.com/tutorials/mass-assignment-rails-and-you--net-31695,
set this in dev and test so that you get explicit mass assignment errors
in dev and test so that it's clearer what's going on and what needs to
be fixed.

Starting a pull req to get travis running with this; i will be adding more commits to this branch in a second that actually make the tests pass, hopefully :)