Add catalog (Producer) zone support.

[gjherbiet]

This pull request aims to bring catalog zones support to dns-ui. They are also internally called "Producer" zones in PowerDNS.

This is currently a work in progress! However, feel free to already review and comment changes.

This is my first large pull-request for this project, so advice on how to contribute in the cleanest way is very welcome!

Planned features:

• [X] Attach existing catalog zone when creating a new zone
• [X] Set or update catalog zone in existing zones configuration
• [X] Create new catalog zones
• [X] Change zone configuration from/to catalog from/to any other type
• [ ] Add catalog zone column in zones listing array
• [ ] Make catalog zones records read-only
• [ ] Display member zones in catalog zone details
  • [ ] (?) Allow to add/remove member zones from catalog zone details
• [ ] Configure default catalog for new zone in settings