common improvements (#366)

- std container replacements for vector, unordered_map, unordered_set
  - unordered_map and unordered_set replaced with ska::flat_hash_map
  - vector replacement is still std::
- unordered_map performance test (std:: vs ska::)
- backlog improvements
- wiArchive improvements
- editor: added option to dump scene to C++ header file
- common improvements, refactors

Editor/MaterialWindow.cpp

@@ -2,8 +2,6 @@
 #include "MaterialWindow.h"
 #include "Editor.h"
 
-#include <sstream>
-
 using namespace wiGraphics;
 using namespace wiECS;
 using namespace wiScene;