proposal: Customise statuses

Proposal would:

1. Allow teams to change the labels of the statuses
1. Allow teams to add extra statuses

This proposal could include one or both of these features.

For example, an agile team might change the labels such that:

* `Future` -> `Backlog`
* `Up next` -> `This iteration`
* `In progress` -> `In progress`
* `+` `In test`
* `Done` -> `Done`