Detect repo re-creation

As a result of discusion in #93, we have identified general issues with collection as it relates to moved/changed repos

this issue happens when:

1. a github repo has been collected on
2. the underlying github repo is *Deleted* (not moved or renamed)
3. the underlying github repo is replaced with a new repo at the same URL
4. Collection runs again

This will pass right through our current repo move detection unnoticed because the same URL is still valid and no redirect will happen.

a specific, non exhaustive list of things that happen as a result:
- attempts to collect on that new repo will fail with an error related to duplicate URLs when collecting pull requests (this is #93)
- presumably the same thing happens with issues too (#151)
- Facade seems to happily clone the new repo - potentially overwriting the previous repo (and creating inconsistent state)