Add ImGui

- Initial ImGui commit, add support for showing demo window in Copium
  Engine

CopiumEngine/src/copium/core/ImGuiInstance.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <memory>
+
+#include "copium/buffer/CommandBuffer.h"
+#include "copium/pipeline/DescriptorPool.h"
+
+namespace Copium
+{
+  class ImGuiInstance
+  {
+    CP_DELETE_COPY_AND_MOVE_CTOR(ImGuiInstance);
+
+  private:
+    std::unique_ptr<DescriptorPool> descriptorPool;
+
+  public:
+    ImGuiInstance();
+    ~ImGuiInstance();
+
+    void Begin();
+    void End();
+    void Render(CommandBuffer& commandBuffer);
+
+  private:
+    static void CheckVkResult(VkResult err);
+  };
+}