This introduces RB.FormView, which is designed to be used with

.rb-c-form classes, and aids in managing forms. Right now, it's pretty

basic, offering only support for expanding/collapsing

.rb-c-form-fieldset components. Down the road, it'll be a useful place

for adding common form functionality that we're otherwise potentially

re-implementing in several other form implementations.
This is currently being used for the Change Form, to implement the

collapsed fieldset support there.

Unit tests passed.
Manually tested this with Change Form.