QRCodes for Direct Install + Install Page

This pull request enables QRCodes and adds two of them to the OTA HTML install page template.
The first QRCode opens the Install Page itself once scanned from a device.
The second QRCode directly asks the user if he wants to install the App on his iPhone/Pad. It behaves like clicking the "install over-the-air" button.

Furthermore I tried to make the default HTML template more dynamic and lean. The QRCodes are displayed when the links are clicked and UI elements not relevant for desktop / device are not displayed.