Implement median filter (#697)

Add median filter to sensors component

tests/test1.yaml

@@ -191,6 +191,10 @@ sensor:
         - 100.0 -> 102.5
       - filter_out: 42.0
       - filter_out: nan
+      - median:
+          window_size: 5
+          send_every: 5
+          send_first_at: 3
       - sliding_window_moving_average:
           window_size: 15
           send_every: 15