add google verification code on homepage

@alexanderadam @effkay pls take a look at this

nothing fancy but needed for hieronymus.

in app/views/kuhsaft/pages/show.html.haml:5 i checked again if we are on the 'homepage' since switching page trees etc can result in more than one page to have the 'google_verificatio_code' attribute set and we dont wat different keys to be rendered.

kind regards