Vib and led brick noflashfix

critical bug solved: app crashed on nexus7 when switching on flash

the problem was, that the API call returned true, if asked for flash availability. the work-around implemented in the function hasFlash() in class PrestageActivity is taken from https://stackoverflow.com/questions/13413938/how-to-check-if-device-has-flash-light-led-android/19599365#19599365

it works on all devices under API 10, 11, 18, 19 (so far)