Prepare for Drupal 8.4

[dannylamb]

Drupal 8.4 has been released: https://www.drupal.org/project/drupal/releases/8.4.0

The major change is that Media have been brought into core. Although mostly a port of the existing Media Entity module, there are likely to be subtle changes. A re-export of configuration (bundles, etc...) is also likely.

This issue exists to track changes we discover that need to be addressed before we can make the switch to 8.4.

[dannylamb]

It looks like our best bet is to stick with media_entity for now, not using the core media module. There's some things like inline forms that haven't caught up yet, and all of what we have works on 8.4.

The main thing we'll have to address is that Files are no longer deleted on cron run in 8.4, so we'll need to manually delete files when we delete their media, which I feel would be a good improvement.

[dannylamb]

Closing for now, and will create new tickets with specifics for porting to core media entities when the time comes.