VCPKG Full refactor

uses local cache for assets now so should be able to produce an offline build with vcpkg. Only a couple of libraries left that are too big, and the vcpkg repo itself has files that are blocked from the repo. We could get around both issues by utilizing a submodule

Engine/source/gfx/bitmap/imageUtils.cpp

@@ -24,7 +24,7 @@
 #include "gfx/bitmap/imageUtils.h"
 #include "gfx/bitmap/ddsFile.h"
 #include "platform/threads/threadPool.h"
-#include "squish/squish.h"
+#include <squish.h>
 
 namespace ImageUtil
 {

Engine/source/gfx/bitmap/loaders/bitmapPng.cpp

@@ -32,8 +32,8 @@
 
 #define PNG_INTERNAL 1
 #include <time.h>
-#include "lpng/png.h"
-#include "zlib/zlib.h"
+#include <png.h>
+#include <zlib.h>
 
 #ifdef NULL
 #undef NULL