Spotler 1.0.0-alpha2: accessibility and config-collision fixes.

Changes since 1.0.0-alpha1:
- Rename field_title to field_spotler_title to avoid config collisions.
- Fix list field allowed_values format and field ownership.
- Fix AJAX feedback and message bleed in SubscribeForm.
- Improve SubscribeForm accessibility and remove themed colors.
- Add Dutch translations for new accessible-name strings.