Added libpng to required packages.
Added libpng to required packages.

amitdo/clstm,tmbdev/clstm,amitdo/clstm,mittagessen/clstm,ryanfb/clstm,mittagessen/clstm,MichalBusta/clstm,kba/clstm,amitdo/clstm,MichalBusta/clstm,amitdo/clstm,tmbdev/clstm,MichalBusta/clstm,ryanfb/clstm,MichalBusta/clstm,jbaiter/clstm,tmbdev/clstm,kba/clstm,jbaiter/clstm,kba/clstm,ryanfb/clstm,jbaiter/clstm,mittagessen/clstm,kba/clstm,tmbdev/clstm,jbaiter/clstm