Add PNG and wxWidgets 3.1.3 uniformly to all platforms with cmake build.

wx is built with png as a dependency, wxpng is disabled.

deps/PNG/PNG.cmake

@@ -0,0 +1,13 @@
+prusaslicer_add_cmake_project(PNG 
+    GIT_REPOSITORY https://github.com/glennrp/libpng.git 
+    GIT_TAG v1.6.35
+    DEPENDS ${ZLIB_PKG}
+    CMAKE_ARGS
+        -DPNG_SHARED=OFF
+        -DPNG_STATIC=ON
+        -DPNG_TESTS=OFF
+)
+
+if (MSVC)
+    add_debug_dep(dep_PNG)
+endif ()