Add status as an option for 'stage'

[mtorres253]

So that project leads can mark their projects as active or inactive, there should be an easy way for them to do this.

Acceptance criteria: I am a project lead My project is defunct, or no longer active I specify in my project stage, that my project is inactive The team API now returns an attribute stage with value inactive.

See https://github.com/18F/concourse-compliance-testing/issues/11 for reference

Need to make sure this doesn't break current validation scripts