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.
Add attr_accessibles for everything we have tests for

This article recommends we prefer the whitelist using attr_accessible
instead of attr_protected:
http://code.tutsplus.com/tutorials/mass-assignment-rails-and-you--net-31695

which sounds like a good idea even though we probably won't be adding
many new attributes.

It looks like radiant implemented their own version of this on User, so
I removed that and made it use the built in rails stuff instead. Good
for them!

There's probably more out there, but the tests aren't showing them to
me. At least the previous commit will make it obvious when we hit them.
Merge pull request #89 from carols10cents/fix-tests

Add a setting in dev and test to make mass assignment errors obvious
Have sass-rails3 only in the gemspec

Since Eric released it as a proper gem, it works fine in the gemspec and
it doesn't need to be in the Gemfile anymore. Yay!!!!