Kernel: namespace and function renames

MMU moved to namespace kernel
Kernel::Memory::Heap moved to just Kernel
MMU::map_{page,range} renamed to identity_map_{page,range}

Add MMU::get_page_flags

kernel/kernel/kernel.cpp

@@ -139,7 +139,7 @@ extern "C" void kernel_main()
 	ASSERT(tty1);
 	dprintln("TTY initialized");
 
-	Memory::Heap::initialize();
+	Heap::initialize();
 	dprintln("Heap initialzed");
 
 	parse_command_line();