Rename namespace class to {package.name}Package

Conflicts:

	compiler/jet.as.java.psi/src/org/jetbrains/jet/asJava/JavaElementFinder.java

compiler/testData/writeSignature/jlString.kt

@@ -1,6 +1,6 @@
 fun string(): java.lang.String = throw Exception()
 
-// method: namespace::string
+// method: _DefaultPackage::string
 // jvm signature:     ()Ljava/lang/String;
 // generic signature: null
 // kotlin signature:  ()Mjava/lang/String;