Add FindPNGwriter Module

... and use it in all CMake Projects
Close https://github.com/ax3l/pngwriter/issues/8
PNGwriter changes very seldom: shared linking

Compared to libSplash, PNGwriter changes very seldom
so that is a good case for shared linking in our
projects to reduce complexity (of double linked
shared/static libraries) with other modules.
Merge pull request #308 from ax3l/topic-FindPNGwriter

FindPNGwriter Module and GOL ICC