Bin metadata

- [ ] Ready to merge

Initial front end to WIP for custom headers, title and description will link to inline HTML.

- [x] Support title & description (should this be connected to the HTML, I think so)
- [x] Save custom header data in bin.settings.headers / statusCode, etc
- [x] Save on change
- [x] Tests
- [x] Custom headers should override default headers - like content type

Fixes #1824