Renaming SDLTest to GraphicStripTest part 1

Renaming of folder and .pro but no modification in the code yet
Renaming SDLTest to GraphicTest
fix SDL compilation on macos
check if image file exists
Merge branch 'mdgraphictest'

* mdgraphictest:
  check if image file exists
  fix SDL compilation on macos
  Renaming SDLTest to GraphicTest
  Renaming SDLTest to GraphicStripTest part 1