Cleanup CmakeLists and require 2.8.5+

- rename deprecated variables:
  - MPI_INCLUDE_PATH -> MPI_C_INCLUDE_PATH
  - MPI_LIBRARIES -> MPI_C_LIBRARIES
  - HDF5_INCLUDE_DIR -> HDF5_INCLUDE_DIRS
- System Libraries:
  - use SYSTEM property
  - LINK_DIRECTORIES is NOT necessary, since FIND_PACKAGE always returns
    absolute paths
    http://cmake.org/cmake/help/v2.8.11/cmake.html#command:link_directories
- fix comment for CUDA_MATH
- rename and invert variable DISBALE_COMPILER_FLAGS_IN_SUBPROJECTS to
  SAME_NVCC_FLAGS_IN_SUBPROJECTS
- hdf5/libSplash
  - remove PIC_ENABLE_HDF5 Option and use HDF5_FOUND
  - check for splash.h and libsplash.a (update your libSplash installations!)
- png output
  - remove PIC_ENABLE_PNG and see if we can find libPNGwriter
  - add freetype finder
Doc: cmake 2.8.5+
Merge pull request #52 from ax3l/fix/CMakeIncl

Cleanup CmakeLists and require 2.8.5+