Add meta data for better sharing

[friedger]

When sharing via G+ or so devfest.gdg.events should show the icon of the tagged event series. Similar for event pages, they should contain relevant meta data.

[mauimauer]

Going to add SEO-Prerendering with PhantomJS (we also need this to be properly indexed by the Googlebot).

[friedger]

@mauimauer has this been added?

[mauimauer]

No...but the implementation could basically be copied over from the Hub.

[Splaktar]

Added a site description and application-name in #41

Boomerang has a way to define a snippet image used for sharing. That could be ported here to help with this.