replace <x-viewmodel-page> with <x-html>
remove `mdv_extra.js` from dependencies of <x-html>, now <x-html> is self sufficient in inserting partial HTML to the document
remove redundant `getModel` function, now model can be accessed using the getter
parse HTML imports found in the partials loaded through `<x-html>`
parse styles found in the partials loaded through `<x-html>`
upgrade json-patch-duplex.js (0.3.6)
upgrade to x-html.html v20131109