Add support for buttons

[MatthewMaclean]

It may be a bit out of the scope of the easy UI editor, but it'd be nice if I could provide a JSON value for a button via id that looking something similar to:

{"id": "<button id>", "value": {"<key in button>": "<value for button>", "<span-id>":"<span content>"}}

I'm trying to autofill a button that isn't making any network calls, it's just saving a data value + updating a span value's view. I get that this is definitely more complicated and freeform than other types of form inputs, so I understand if it's out of scope or too niche to maintain.