Change task Requiered Altitude Calculation :
if next Tp Requiered Altitude is less than current tp altitude, use current tp altitude for requiered altitude...
 - AAT Task : altitude of AAT Target point is used if upper center altitude, otherwise, center altitude is used.
 - PG optimized : always use Optimized point altitude. (reverted from commit 14c9a655a322867ee7f8643a1548078100dc22e4)
Fix Glide Bar should not be visible when there is no valid start, if it is configured to show task arrival altitude.
Beside, the value shown without a valid start was wrong.