Feature #298 media list usage display

[ekes]

Adds an alternative admin view for admin media page including a usage column.

Update hook will replace view if it's not been changed (and entity_usage is installed).

Manual tests:

• Install fresh: /admin/content/media should have a usage count column;
• Install on existing site: if the /admin/content/media view has not been changed it will be update; if it has been changed it should not be updated; if entity_usage is uninstalled it should not be updated.

Note about automated tests: This suffers from the same issues as #297 (comment) We should move these functionalities elsewhere at some point and work out how to make reliable tests.

[ekes]

[markconroy]

Works a treat on a new install.

[tonypaulbarker]

This is a nice enhancement. For follow up, wondering if it would work to display a link (or the list of items) on the media entity edit pane so people could see the usage at the point of editing.

[markconroy]

@tonypaulbarker Good idea. Wanna create a new issue for that and we can work on it then?

[tonypaulbarker]

Follow up issue created at #300

[willguv]

@ekes @tonypaulbarker I'd like to write about this in the next product newsletter (goes out first week of the month)

How do users get this please?

• ensure entity_usage is installed (think this should be in the profile, is it?)
• update localgov_core?