fixed two bugs in ActivityButterPressure:

1) when barometer produces false measurements, we needed some kind of upper boundary
2) coding error static.. while initializing this object over multiple test iterations isnt the best idea

sensors/activity/ActivityDetector.h

@@ -140,7 +140,7 @@ private:
 			++xx;
 		#endif
 
-		if (std::abs(delta_hPa) < 0.042) {
+        if (std::abs(delta_hPa) < 0.042) {
 			current = Activity::WALKING;
 			return;
 		} else if (delta_hPa > 0) {