replace obsolete logic for meta tags with include provided by devsite, and add data attributes to the ReferenceObject itemprop tag that carry api level information for the future version of the API level selector. Note that if the build specifies 'library.root' then that is still used to specify the _book.yaml location in a django variable. This way, we still have control from the DevSite include as to whether we use it.
am: ae14dffd83

Change-Id: Ie50e9540b51b4a97e4dc060326b1648d1aad379d