Finalize polyfill choices

[erutan]

https://afarkas.github.io/webshim/ is the "default" for HTML5 forms - you can modularize it fairly well, but has a (relatively) hefty page load. could load it from inside a yep/no?

aside from client side validation, we could pretty get away with just a placeholder polyfill w/ modernizr check, which is a lot lighter.

authoritative list @ https://github.com/Modernizr/Modernizr/wiki/HTML5-Cross-browser-Polyfills#web-forms

this can be pushed until later, and will be impacted by final browser support choice

[erutan]

webshim it's looking to be, due to ok to fit in client side validation