Convert PasswordFields to GovukPasswordFields

Converts them directly in the following forms:
- LoginForm
- ConfirmPasswordForm

Changes the password function to return
GovukPasswordField instead of PasswordField which
effects the following forms:
- RegisterUserForm
- RegisterUserFromInviteForm
- RegisterUserFromOrgInviteForm
- NewPasswordForm
- ChangePasswordForm

It also updates StringField on RegisterUserFromOrgInviteForm
to GovukTextInputField

Also includes changes to templates that use this
form and associated tests.

app/templates/views/user-profile/authenticate.html

@@ -19,7 +19,7 @@
     <div class="govuk-grid-column-three-quarters">
 
     {% call form_wrapper(autocomplete=True) %}
-      {{ textbox(form.password, autocomplete='current-password') }}
+      {{ form.password(param_extensions={"autocomplete": "current-password"}) }}
       {{ page_footer('Confirm') }}
     {% endcall %}
     </div>