Add ImGui

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

CopiumEngine/src/copium/pipeline/DescriptorPool.cpp

@@ -47,4 +47,9 @@ namespace Copium
   {
     vkFreeDescriptorSets(Vulkan::GetDevice(), descriptorPool, descriptorSets.size(), descriptorSets.data());
   }
+
+  DescriptorPool::operator VkDescriptorPool() const
+  {
+    return descriptorPool;
+  }
 }

CopiumEngine/src/copium/pipeline/DescriptorPool.h

@@ -18,5 +18,7 @@ namespace Copium
 
     std::vector<VkDescriptorSet> AllocateDescriptorSets(VkDescriptorSetLayout descriptorSetLayout);
     void FreeDescriptorSets(const std::vector<VkDescriptorSet>& descriptorSets);
+
+    operator VkDescriptorPool() const;
   };
 }