Add paperclip icon to multimedia case properties
Fail multimedia case properties on CommCare <= 2.5

External media questions should not be able to be selected as a valid input type to the case property saving UI if the current project is set to CommCare 2.5 or below.
Improve XML diff output

- Normalize attribute sort order to reduce noise.
- Fix argument order in FormPrepBase.assertXmlEqual super call, which corrects the Got/Want labels.
- Remove extra newlines (double-spaced lines).
Generate attachments in case XML