Feature/identity specs

This is a pretty big commit and includes most of the specs required to test requests and model. I'm finishing up models, but wanted to go ahead and get it out for review. To be honest, most of the admin API stuff probably won't get used that much anyway.

Feel free to raise issues and I'll address. Hopefully we can gain consensus around this and move on next week.

Bear in mind that this PR is a bit chaotic given the need for refactoring in almost every corner of this codebase... so be kind. ;-)