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
basic dropdown experiment
Merge remote-tracking branch 'origin/master' into mmcp2-base
Prefix upload props in Case List with attachment:
attachment: case property prefix on all form types
Cleanup/code simplification
Add icon on attachment case list suggestion columns
Add "picture" format to case detail list
Add note about running subset of tests in README
Add support for picture format in case list detail
Add support for "attachment" xpath field type
Fix minimum version for MM case properties
Small cleanup

- Clean up HTML/CSS
- Remove superfluous if block
- Remove TODO comment
convert links to static assets to dynamic
add doc_info processor for showing usernames in case detail
update to pretty-user-display branch of casexml
specify endblocks to make templates easier to read