Make the hierarchical multiselect a more modular datatype

[nonprofittechy]

Currently the major issue is that you need to invoke the JavaScript manually on each input you want transformed with the multiselect code. There are a few ways to fix this--one simple way might be to transform all multi-selects (it's not a commonly used input type in DA interviews). Another might be to tell people who want to use this input to add a custom CSS class on that input, now that Docassemble lets you do that arbitrarily.

Either way a bit of new JS needs to be added to run the multiselect transformer on each of the inputs we decide need it. Possibly best to add an additional JS file to hold this code.