frontend: refactor createFormValidator

[alee]

right now the createFormValidator works but is a bit of a convoluted mess that is possibly only understood by @cpritcha. We should see if there are better ways of abstracting its responsibilities:

1. form validation
2. others?

[alee]

as a first step we probably need to just document it better so that we can figure out how to use it properly. I think we figured this out as needing to modify the yup() schema

overall https://github.com/jquense/yup is pretty nice, and the abstractions make sense after looking at it for a while but we should still figure out areas of clean where possible