format: Refactor format factory to non-static class

The format factory can be based on the abstract factory class if it
wasn't static. This allows for higher abstraction and makes future
extensions possible. Also, not all parts of RSS-Bridge need to work
on the same instance of the factory.

References #1001

lib/BridgeList.php

@@ -63,9 +63,11 @@ EOD;
 
 		$bridgeFac = new \BridgeFactory();
 		$bridgeFac->setWorkingDir(PATH_LIB_BRIDGES);
-
 		$bridgeList = $bridgeFac->getBridgeNames();
-		$formats = Format::getFormatNames();
+
+		$formatFac = new FormatFactory();
+		$formatFac->setWorkingDir(PATH_LIB_FORMATS);
+		$formats = $formatFac->getFormatNames();
 
 		$totalBridges = count($bridgeList);