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.

tests/app/main/views/organisations/test_organisation.py

@@ -1132,8 +1132,8 @@ def test_confirm_update_organisation_with_incorrect_password(
     page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
 
     assert normalize_spaces(
-        page.select_one('.error-message').text
-    ) == 'Invalid password'
+        page.select_one('.govuk-error-message').text
+    ) == 'Error: Invalid password'
 
 
 def test_confirm_update_organisation_with_name_already_in_use(