Facebook Open Graph metadata

It misses the 'title' property, unfortunately, as those are stored in
the templates themselves. I don't think that will be much of an issue,
though.
HTML5 doctype
Use the right language attributes (nl-NL)
Specify charset in HTML
Add 'initial-scale=1' to viewport meta tag

This ensures the webpage always scales properly on iDevices.
Merge pull request #220 from aykevl93/metadata

Metadata (o.a. Facebook Open Graph)