take initial tilt as default

[niosus]

For now the app works by tilting the phone from the horizontal position. However, this is not the way we use smartphones. We usually look at the smartphone in an already tilted state (pitched to approx 45 degrees) and then we tilt it from this initial position. It would be cool to make the app remember the initial position and to move the map accordingly.

[petervojtek]

I confirm this will be more comfortable. however it will need some better tutorial/videos on how to use the app.