Implement cache invalidation

• Simplify API call → renamed method names
• Process to invalidate cache
  • Retrieve new list of projects through group/:id call
  • Loop through all projects and invalidate old cache whether cache is still up to date
    • Compare timestamp last_activity_at with the timestamp on the local file.
    • Implement a call to invalidate cache files for a whole project?
      There are multiple cache files linked to a project
      • commits
      • tree
      • possibly raw's
        • Do a sort of stat on the API through the file endpoint to lookup which commit lastly changed the file.
          • Test if this works for directories.
  • Map which feeds to update
    • Atomic updates of listings → replace / extend list of commits to not have to go through all pages.