Admin-user can edit work body/content

[quivop]

User story

As an admin user, I want to edit my work's content to change what is displayed.

Acceptance criteria

• Start from work editing form
• Select particular work content part
• Go to work part editing page
• Change the work part title or body text
• Submit the changes and see them reflected on the site

[netahe]

I believe both this issue, and Admin-user can edit work metadata should be split into smaller tasks.

1. implement CRUD operations for work/part/metadata (in the form of HTTP GET/POST/PUT/DELETE)
2. Create editor page for work/part/metadata

[quivop]

Django's admin modules actually do all the CRUD stuff and provide an editing page by default. What's left to sort out this issue is to implement tests that verify that all that stuff works correctly.