New feature: Apply channel defaults

Summary

Add "Apply channel defaults" feature that will apply channel defaults to the channel resources.

Requirements

• A possibility to apply channel defaults to all nodes of a channel
• A possibility to apply channel defaults to a node being edited in the edit modal
• Notify users about this feature. We've located two places where it might be suitable:
  (1) Before publishing a channel when some problems are found (in publish modal, might overlap with #2926)
  (2) It seems that our users won't even try publishing if there are many errors displayed on the channel editor page. That's why, in addition to (1), it would be good to recommend this feature if we detect some problems when the channel editor page is open.
  We would need to specify criteria for showing these recommendations (e.g. majority of resources on the page is erroneous, or has exactly the same problem, for example with license..??)

Implementation notes

@rtibbles mentioned that we might use tasks.

Real-life consequences

The initial motivation for this feature are historical data that have missing license information. If there are many resources in a channel with this problem, a user would need to fix it one by one. We would like to make this easier. Having this functionality would be useful in general.

Start with the channel editor page, node edit modal, and publish modal, then review the suggested task-based implementation. Done means users can apply channel defaults to every node or the node being edited, and receive recommendations at the relevant editor or publishing points using explicit criteria.