Style: Cleanups, added headers, renamed files

Made sure files in core/ and tools/ have a proper Godot license header
when written by us. Also renamed aabb.{cpp,h} and object_type_db.{cpp,h}
to rect3.{cpp,h} and class_db.{cpp,h} respectively.

Also added a proper header to core/io/base64.{c,h} after clarifying
the licensing with the original author (public domain).

core/resource.cpp

@@ -27,12 +27,14 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 #include "resource.h"
+
 #include "core_string_names.h"
-#include <stdio.h>
 #include "os/file_access.h"
 #include "io/resource_loader.h"
 #include "script_language.h"
 
+#include <stdio.h>
+
 void ResourceImportMetadata::set_editor(const String& p_editor) {
 
 	editor=p_editor;