Require email address for reporting problems

If you report a problem we want to be able to get back to you to find
out more information, or to update you on the status of a fix. So it
shouldn’t be possible to report a problem without providing an email
address.

This commit makes `email_address` a required field when `ticket_type` is
problem.

This requires a bit of fiddling with the tests which weren’t expecting
to have to provide an email address. So the tests now either:
- pass an email address
- check for an error when they don’t pass an email address

app/main/forms.py

@@ -403,12 +403,16 @@ class SupportType(Form):
     )
 
 
-class Support(Form):
+class Feedback(Form):
     name = StringField('Name')
     email_address = StringField('Email address')
     feedback = TextAreaField('Your message', validators=[DataRequired(message="Can’t be empty")])
 
 
+class Problem(Feedback):
+    email_address = email_address(label='Email address', gov_user=False)
+
+
 class Triage(Form):
     severe = RadioField(
         'Is it an emergency?',