Make the UI for managing scheduled posts behave similarly to the UI
for managing drafts:

- Instead of an edit button, tapping a scheduled post edits it.
- Tapping a post already in an editor moves that editor task to the
front, instead of launching a new one
- Instead of a delete button, show a checkbox to select the post (allow
multiple selections). This starts an action mode, allowing the user to
delete multiple posts at once.
- Show content warnings, attachments, and polls