Update labels for all open tickets

[ehmatthes]

Task

• [x] Label all open issues that need to be completed for 1.0.
• [x] Add plugin label to any label relevant to implementing a plugin model.

[ehmatthes]

Notes

• Closing many issues that might come up again, but are so old they were raised when the project was in a quite different state. If those issues are still relevant, they'll be better served by making a new issue when it comes up again.