Repository based authorization

* Public repos read permission granted to all authenticated users
* Public repos all other permissions limited to collaborators
* Private repos all permissions limited to collaborators
* Non Git jobs & git jobs with no repository configured are not affected
User controllable flag to enable/disable reposistory authorization

When not enabled backwards compatible with old version
removed innacurate copyright notice
removed some unnecessary lines in tests
fixed bug with empty git repository url causing NullPointerException
Merge pull request #17 from alexrothenberg/repo-level-authorization

Repository based authorization