Collecting the following updates: - Added a FindPNG.cmake module to AtlasLCG, and made sure that it would be able to find the PNG library from the LCG release; - Added libxml2 to AnalysisBaseExternals, and made the ROOT build make use of it; - Stopped the ROOT build from looking for BLAS, as that makes the build depend way too much on libraries available only on lxplus; - Made the dictionary generation code more robust in the CI system.