Reusables save behavior weird

[alondhe]

Expected behavior

Reusable designer should behave like other modules: clean saving, saving when changes are detected.
When importing a reusable that leverages a source concept attribute, this should import cleanly.

Actual behavior

It's been hard to pin down, but we've seen Reusables save state behavior not functioning well: save button not appearing when it should, the JSON isn't saving cleanly. Bringing these into cohorts isn't always being imported cleanly, particularly when there's a source concept attribute.

Steps to reproduce behavior

Create a reusable, start adding content, see that the save button isn't always enabled when changes are made.

Tagging @konstjar