Add POCSAG processing and display code.

Nextion.h

@@ -68,6 +68,9 @@ protected:
   virtual void writeNXDNBERInt(float ber);
   virtual void clearNXDNInt();
 
+  virtual void writePOCSAGInt(uint32_t ric, const std::string& message);
+  virtual void clearPOCSAGInt();
+
   virtual void writeCWInt();
   virtual void clearCWInt();