In multi-select fields, don't try to coerce every option to an object on form load

[Nick Harvey]

Forms containing a multi-select field with a large number of options can be very slow to load. Instead of creating an object for every option, return the id of the object so it can be looked up later, if selected or evaluated.

One example of this fix is here:

https://github.com/level12/gb-h2r/pull/160/commits/b34cd3a680aafac8336f9d7f73582975004d00c7