Improves build process for internal development

Adds an INTERNAL preprocessor definition to manage dependencies.

This change allows for a lighter build during internal development by
forward declaring some classes and excluding UI and CAN dependencies.

server/simulator_base.cpp

@@ -1,4 +1,6 @@
+#define INTERNAL
 #include "simulator_base.hpp"
+#include "ui_item.hpp"
 
 Simulator_base::Simulator_base(std::string name, Communication *com, std::chrono::milliseconds interval,
                                QObject *parent)