Comment 10 for bug 1751353

I've pushed a cursory branch here: https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/khuckins/lp1751353-patron-statcat-tts

We identified that the original javascript-side of this was lost in a git mishap, so I've reworked the branch from scratch.

There are a few issues with eg-combobox not wanting to find the correct values. Those issues are addressed in 1819233, which has been signed-off on.

The last remaining piece of this is to add handling of invalid values - a blank field will fail due to a null value, but a value that isn't on the list will save just fine, which probably isn't ideal.