Whitespace cleanup

* remove trailing whitespace
* remove empty lines at the end of files

plugins/wifi/wifi_signal

@@ -24,7 +24,7 @@ do_config () {
     echo "graph_vlabel dB"
     echo "graph_category wireless"
     echo "graph_info This graph shows the noise and singal levels of your WiFi devices"
-    
+
     awk -F'[ :]*' '/:/ {
 	        print $2"_noise.label Noise "$2;
 	        print $2"_signal.label Signal "$2;