Add support for recording github repo ID/node id

[mrzarquon]

While we access and work with repos by name, a repository can be renamed, but the id and node id should remain the same. We should record those for future uses of detecting a renamed (instead of one repo removed, one added) repo:
API Snippet:

"id": 1296269,
"node_id": "MDEwOlJlcG9zaXRvcnkxMjk2MjY5"

[mrzarquon]

#14 added support for tracking repo ID's if they show up in the targets payload, may need adjusting when they go live

by default we search by repo IDs, then fall back to repo full_name