Use jQuery to build DOM elements instead of string concatenation

Took a swing at https://github.com/powmedia/backbone-forms/issues/406

All the tests are still passing.

This probably demands new tests that ensure it's properly encoding special characters.

Also, as this will frequently be MUCH slower than string concatenation, should these editors (or the top schema) have a 'trustedContent' flag or something similar? That would then use string concat instead?

It probably wouldn't ever matter. "This isn't the bottleneck you're looking for", etc.