Shell + page loading

And:
- some basic stylesheet i found for basic html elements
- a global lua method for navigating pages

src/app.hpp

@@ -0,0 +1,56 @@
+#pragma once
+
+#include <RmlUi/Core/Context.h>
+#include <RmlUi/Core/ElementDocument.h>
+#include <RmlUi/Core/EventListener.h>
+#include <string>
+#include <type_traits>
+#include <vector>
+#include <memory>
+#include <functional>
+#include <unordered_map>
+#include "page.hpp"
+
+struct ApplicationData {};
+
+class App {
+public:
+    App(Rml::Context* ctx, ApplicationData* appData);
+    ~App();
+
+    void SetupListeners(std::function<void(Rml::ElementDocument*)> bindCallback);
+    void RegisterListener(Rml::Element* element, std::unique_ptr<Rml::EventListener> listener);
+
+    template <typename T = PageBase>
+    void RegisterPage(const std::string &pageName) {
+        static_assert(std::is_base_of<PageBase, T>::value, "T must derive from PageBase");
+        pages[pageName] = std::make_unique<T>(pageName, this);
+    }
+
+    bool NavigateTo(const std::string &pageName);
+    
+    bool LoadUi();
+    void Reload();
+
+    static std::string GetAssetsPath();
+
+    void Shutdown();
+
+private:
+    ApplicationData *appData;
+    Rml::Context* ctx;
+    Rml::ElementDocument* doc;
+    Rml::Element* pageOutlet = nullptr;
+
+    std::vector<std::unique_ptr<Rml::EventListener>> listeners;
+    std::function<void(Rml::ElementDocument*)> onBindListeners;
+
+    std::unordered_map<std::string, std::unique_ptr<PageBase>> pages;
+    PageBase* currentPage = nullptr;
+
+    PageBase* GetOrCreatePage(const std::string& pageName);
+    static bool ReadFile(const std::string& path, std::string& outContent);
+    void TeardownCurrentPage();
+
+    bool hasShutdown = false;
+};