Replace gmaps-link by popup with qrcode and links

If you want to use your smartphone for navigation, you can now just scan
the qr-code and (if your scanner-app supports it) directly input the
locations to your navigation-app.
Additionally a link to the location in gapps and OSM will be displayed.
Make changes asked by breunigs
Add Merovius to contributors
Merge pull request #307 from Merovius/qrcodes

Replace gmaps-link by popup with qrcode and links