Add metrics which leverage registration data

[brendanheywood]

• [ ] this needs to work even if the site isn't registered Add these metrics: (these should be all 'registration' ones but if some aren't lets split those into other issues)

• [ ] Number of users (138371)

• [ ] Number of recently active users (18095)

• [ ] Number of role assignments (971597)

• [ ] Number of posts (392798)

• [ ] Number of questions (7099796)

• [ ] Number of resources (214837)

[jaypha]

Any suggested colours?

[brendanheywood]

Ah! sorry we already have this data, I'm cancelling this one sorry