enable photo traits with brapi

[lukasmueller]

Description

Enable photo traits with brapi. Set trait_format to 'photo'.

Also, hide trait properties section for traits; only show for variables. Maybe this section should be renamed...

Checklist

• Refactoring only
• Documentation only
• Fixture update only
• Bug fix
  • The relevant issue has been closed.
  • Further work is required.
• New feature
  • Relevant tests have been created and run.
  • Data was added to the fixture
    • Data was added via a patch in /t/data/fixture/patches/.
  • User-Facing Change
    • The user manual in /docs has been updated.
  • Any new Perl has been documented using perldoc.
  • Any new JavaScript has been documented using JSDoc.
  • Any new legacy JavaScript has been moved from /js to /js/source/legacy.

[bellerbrock]

Tested with sptest and this trait,, it works!

It's outside the scope of this PR I think, but it'd be good to make the variable properties handling more sophisticated. Right now it is possible to add more than one trait format (though only the most recently added is shown in brapi). And the format is not restricted to subset of valid formats, but seems to accept any text input.