Add SmBoP to demo

[epwalsh]

From @OhadRubin's work https://github.com/OhadRubin/SmBop, see the discussion here and the Google Colab demo here.

This is a SQL semantic parsing demo where the user picks out of a dropdown menu a schema from Spider and is shown the structure. The user inputs a natural language question where the output is raw SQL. (allenai/allennlp-gallery#40 (comment))

@jonborchardt, @codeviking, I could handle the back-end, but the front-end is probably beyond me. Would one of you be able to help with the front-end? Does it sound doable?

[jonborchardt]

i am happy to help. looking through the docs, im not sure what is needed.
@epwalsh can you distill what is needed for the ui?

[OhadRubin]

@epwalsh Can I help somehow to make this go a bit faster?

[epwalsh]

Hey @OhadRubin, sorry for the radio silence. Our other semantic parsing demos were removed a little while back before we did a major refactoring of the front-end. Unfortunately this means that adding a semantic parsing demo right now would involve a substantial amount of front-end work. So we're going to have to table this for now 😒