fixed some issues with stats::variance

fixed umbrella header for stats
added error-feedback to wifi optimizers
improved logging for wifi optimizers
adjusted calling-API for wifi-optimizers

math/stats/Variance.h

@@ -37,7 +37,7 @@ namespace Stats {
 
 		/** get the current stadard-deviation */
 		Scalar getStdDev() const {
-			return std::sqrt(get);
+			return std::sqrt(get());
 		}