New getHTML() method for QuickTemplate to get the HTML of a template.

OutputPage's addTemplate() is now a wrapper around QuickTemplate.

This allows more flexible usage of templated HTML, as
required by some third-party extensions.

Change-Id: I943e8e50438c716b7b56d2f908da38a4bf73d9e2
Merge "New getHTML() method for QuickTemplate to get the HTML of a template."