Added Html::radio, Html::check, and Html::label.

Migrated some convenience functions from the Xml
class to Html so they can be used. Only added
functions that acted as more than just a wrapper
for another function.

Change-Id: I4cc5876d4be6e04ec554444242cc049a3cff0f58
Merge "Added Html::radio, Html::check, and Html::label."