add remote gpio control as an example plugin

https://github.com/meshtastic/Meshtastic-device/issues/182

src/plugins/RemoteHardwarePlugin.h

@@ -0,0 +1,24 @@
+#pragma once
+#include "ProtobufPlugin.h"
+#include "remote_hardware.pb.h"
+
+/**
+ * A plugin that provides easy low-level remote access to device hardware.
+ */
+class RemoteHardwarePlugin : public ProtobufPlugin<HardwareMessage>
+{
+  public:
+    /** Constructor
+     * name is for debugging output
+     */
+    RemoteHardwarePlugin() : ProtobufPlugin("remotehardware", PortNum_REMOTE_HARDWARE_APP, HardwareMessage_fields) {}
+
+  protected:
+    /** Called to handle a particular incoming message
+
+    @return true if you've guaranteed you've handled this message and no other handlers should be considered for it
+    */
+    virtual bool handleReceivedProtobuf(const MeshPacket &mp, const HardwareMessage &p);
+};
+
+extern RemoteHardwarePlugin remoteHardwarePlugin;