Added Plugin support (#102)

* Build refactoring and initial plugin support

* Possibly fixed linux / mac build

* Added libdl to libglad build script

* Add glfw to imgui dependencies

* Refactored common functionality into "libimhex" for plugins

* Added plugin loading and example plugin

* Added proper API for creating a custom view and a custom tools entry with plugins

plugins/libimhex/source/helpers/event.cpp

@@ -0,0 +1,25 @@
+#include "helpers/event.hpp"
+
+namespace hex {
+
+    void EventManager::post(Events eventType, const void *userData) {
+        for (auto &handler : this->m_eventHandlers)
+            if (eventType == handler.eventType)
+                handler.callback(userData);
+    }
+
+    void EventManager::subscribe(Events eventType, void *owner, std::function<void(const void*)> callback) {
+        for (auto &handler : this->m_eventHandlers)
+            if (eventType == handler.eventType && owner == handler.owner)
+                return;
+
+        this->m_eventHandlers.push_back(EventHandler { owner, eventType, callback });
+    }
+
+    void EventManager::unsubscribe(Events eventType, void *sender) {
+        std::erase_if(this->m_eventHandlers, [&eventType, &sender](EventHandler handler) {
+            return eventType == handler.eventType && sender == handler.owner;
+        });
+    }
+
+}