Let app survive screensaver

[LorenzMeier]

Currently the app stops if the screensaver enables. This may have adverse consequences during flight, as suddenly position information is lost. Could we please allow the app to continue to run even if the screen is locked?

[bblodget]

I committed a change that will keep the screen on while the app runs. Let me know if that works.

It would also be possible to keep the cpu on and let the screen sleep using a WAKE_LOCK. After some searches it appears that keeping the screen on is the more preferred solution because it is automatically managed. If the WAKE_LOCK is not released properly it can cause problems.

https://developer.android.com/training/scheduling/wakelock.html