Removed exceptions, found a better way to handle them.

Refactored the forms so that fields like email_address can be used in multiple forms.
Refactored form validation so that a query function is passed into the form to be run, this
way the form is not exposed to the dao layer and the query is more efficient.

This PR still requires some frontend attention. Will work with Chris to update the templates.

tests/app/main/test_validators.py

@@ -1,10 +1,9 @@
-from pytest import fail
-
+from app.main.dao import users_dao
 from app.main.forms import RegisterUserForm
 
 
 def test_should_raise_validation_error_for_password(notifications_admin):
-    form = RegisterUserForm([], [])
+    form = RegisterUserForm(users_dao.get_user_by_email)
     form.name.data = 'test'
     form.email_address.data = 'teset@example.gov.uk'
     form.mobile_number.data = '+441231231231'