Set title tag based on page metadata

[dylans]

Currently every page on the Dojo website has the same title tag, so everything just says dojo.io.

We should infer a page title from the metadata we have about each page.

[matt-gadd]

@dylans good catch, I think this could potentially be a good issue on dojo/framework for the router to support perhaps?

[KaneFreeman]

Dependent on dojo/framework#601 (PR: dojo/framework#620)