Flickr sync should throw an error if the token permission has been revoked

[Christopher Adams]

While Flickr photo sync and contact import check if the user has a service token, they do not check whether this token is indeed valid.

When the token is invalid, both methods complete with no error and only report that no new photos or contacts were imported. The user has no way of knowing that an error occurred.

Instead, each method should check that the user has a Flickr service token and that the token is valid. If the token is invalid, the methods should report an Error to the user, remove the photo sync and contact import tasks, and set the Flickr connection task to "new".