Rename namespace class to {package.name}Package

Conflicts:

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

compiler/testData/writeSignature/NonGeneric.kt

@@ -1,6 +1,6 @@
 fun foo() = 1
 
-// method: namespace::foo
+// method: _DefaultPackage::foo
 // jvm signature:     ()I
 // generic signature: null
 // kotlin signature:  ()I // TODO: need to skip kotlin signature