Rename Executor to JSExecutor

Summary:
* Cleanup some header files so we use more forward declarations
* Rename Executor to JSExecutor.h
* Move some typedefs to more appropriate locations

Reviewed By: mhorowitz

Differential Revision: D5301913

fbshipit-source-id: e75154797eb3f531d2f42a5e95409f4062b85f91

ReactCommon/cxxreact/CxxNativeModule.cpp

@@ -9,6 +9,7 @@
 
 #include "JsArgumentHelpers.h"
 #include "SystraceSection.h"
+#include "MessageQueueThread.h"
 
 using facebook::xplat::module::CxxModule;