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/new-password.html

@@ -1,5 +1,4 @@
 {% extends "withoutnav_template.html" %}
-{% from "components/textbox.html" import textbox %}
 {% from "components/page-footer.html" import page_footer %}
 {% from "components/form.html" import form_wrapper %}
 
@@ -19,7 +18,7 @@
         You can now create a new password for your account.
       </p>
       {% call form_wrapper() %}
-        {{ textbox(form.new_password, hint="At least 8 characters") }}
+        {{ form.new_password(param_extensions={"hint": {"text": "At least 8 characters"}}) }}
         {{ page_footer("Continue") }}
       {% endcall %}
     {% else %}