Config.js do not have an html validator

[carloslancha]

One of the param types for soy templates is html, and that's being validated by soy checking if it's a string, a function, or a couple more things. So the first we could think to do is to validate it in the same way, but I don't know which would be the behaviour for JSX or other implementations.

We need to figure out a validation for html parameters that could works with all of them.

Thanks!