Poll remote repositories for packages and sync with Skipper's content

[markpollack]

Remote repositories are currently only synchronized with Skipper on server startup. Create a scheduled method that will poll these servers to keep package contents in sync in the background.

Expose a property to control the polling frequency.

Add a repo update --repo-name command to force the updating of package metadata for an existing repo.

When adding a new remote repository, also sync it's metdata contents.

[aweeks-clgx]

Also on this when repo delete should remove the packages that it references.
(repo --update * would also do this).

[sabbyanandan]

The project has evolved significantly since when this issue was created - closing it as invalid.