Update multiselect hash to require key names

Instead of "{foo,bar}" you need to say "{foo: foo, bar: bar}".
This makes it easier when you have more complicated non branched
expressions, for example:
"{foo: foo.bar.baz[0], first_state: states[0].name}"
Merge branch 'explicit-multiselect' into develop

* explicit-multiselect:
  Update multiselect hash to require key names