RegisterFormMixin can now to_dict all fields.

It adds a to_dict function that uses inspect to add all wtf Field
to the returned dict. This allows extensions to the register form
to easily add fields that will be passed to the datastore's
create_user function.
Configurable forms, issue:49
Fix to RegisterForm.to_dict.

Only add fields that are also attributes on the
datastorage.user_model.
Make test_app take kwargs
Views get forms from _security
All unit-tests for configurable forms
Add kwargs for configurable forms.

Specifically list out the kwargs so we'll get an interpreter error
on a bad name.
Merge pull request #58 from eskil/registerform

Configurable forms