renaming the pattern loader to denote that it's just for partials

Author: dmolsen

src/PatternLab/PatternEngine/Twig/Loaders/Twig/PatternLoader.php renamed to src/PatternLab/PatternEngine/Twig/Loaders/Twig/PatternPartialLoader.php

@@ -15,7 +15,7 @@
 
 use \PatternLab\PatternEngine\Util;
 
-class PatternLoader implements \Twig_LoaderInterface, \Twig_ExistsLoaderInterface {
+class PatternPartialLoader implements \Twig_LoaderInterface, \Twig_ExistsLoaderInterface {
 
 	/** Identifier of the main namespace. */
 	const MAIN_NAMESPACE = '__main__';