Add MiddlewareSymbol to EmbeddedMontiArc

Directory: https://git.rwth-aachen.de/monticore/EmbeddedMontiArc/languages/EmbeddedMontiArc/tree/master/src/main/java/de/monticore/lang/embeddedmontiarc/tagging/middleware It should contain all information you need to generate a publisher/subscriber that connects a topic/service to a port. It should be similar RosConnectionSymbol(e.g. extends MiddlewareSymbol) Also adapt EMAPortSymbol and EMAPortInstanceSymbol(see isRosPort)

Remember to create a merge request and assigne it to me