[Interface] Remove post list lock icon and update lock text

[maxschmeling]

• Make it clear that there is a user(s) within the post (current behaviour) but avoid showing a lock icon, since they can potentially still collaboratively edit.
  • Do we need to name the user? Currently, knowing which user is editing is useful since you may wish to contact them out-of-band to coordinate your workflow. Is that still useful or desired?
• Change text to collaborate or join when another user is editing.