Use standard WTForm validation for 'register' page.

[jcass77]

This PR simplifies the /register view so that it makes use of the standard WTForm validation rules.

Why this is necessary:

The way the code is written now, the InputRequired validator is never added to the WTForm field, and validation is done in a non-standard way in views.register. This makes it difficult for users to add their own form validation processing (e.g. using a macro as suggested in the Flask documentation), because field.errors will never be set.

Changes include:

• WTF field requirements are now read directly from STORMPATH_ENABLE_%s and STORMPATH_REQUIRE_%s
• ensure that python setup.py test will only be run for the application's test folder (runs all tests on the Python path otherwise (!?))
• fix test that was ignoring 'username' field requirements

[jcass77]

I took the liberty of also adding the Email and EqualTo validators, and more appropriate validation error messages for each field.

[rdegges]

This is awesome, thanks so much!