[Bridge] Use static variable in listBridges()

This prevents the function from re-loading the same data over and over
again. Instead the same data is returned on each call, during a single
request.

lib/Bridge.php

@@ -70,7 +70,10 @@ EOD;
 	* @return array List of the bridges
 	*/
 	static public function listBridges(){
-		$listBridge = array();
+
+		static $listBridge = array(); // Initialized on first call
+
+		if(empty($listBridge)) {
 			$dirFiles = scandir(self::getDir());
 
 			if($dirFiles !== false) {
@@ -80,6 +83,7 @@ EOD;
 					}
 				}
 			}
+		}
 
 		return $listBridge;
 	}