Update our documentation

[bnjns]

In light of the move to GitHub and the approval of the move to an API and SPA I have updated our various documentation.

This includes:

• An update to the ticket lifecyle, including the addition of a "triage" stage
• A small update to how we use labels (the addition of needs labels)
• A massive overhaul of the tools we use
• A massive overhaul of the development workflow, including how to get things released
• Explicit guides on reporting issues and using forks for small changes to copy
• Added a little bit of detail on v5 now that it's been confirmed

This is probably best reviewed by looking at the files in the branch, rather than the diff.