Modern CMake3 Scripts

[ax3l]

Modernizes our CMake build infrastructure.

Adds:

• targets
• SplashConfig.cmake package for downstream projects
• make test support
• Alex Grund to (previous) developers

Removes:

• the need for a FindSplash.cmake script in downstream projects
• TOOLS_MPI: depends on Splash's MPI support now

Changes:

• libSplash.[a|so] (with a big "s")
• only build shared or static one at a time, default static, changed via -DBUILD_SHARED_LIBS=ON
• CMake options that are optional can be controlled via -DSplash_USE_XYZ=<AUTO;ON;OFF>, default AUTO
• CMake options that are on/off can be controlled via -DSplash_HAVE_XYZ=<ON;OFF> (and are set for the _USE options automatically)
• Use as many dependencies via targets as possible, e.g. MPI (CMake 3.9+ feature)
• Needs CMake 3.10+ due to recent bugs in FindHDF5.cmake for both the C API and the PARALLEL API of HDF5
• internal debug symbols for the (few) HDF5 checks are automatically enabled on Debug builds
• Debug builds are now controlled via the standardized -DCMAKE_BUILD_TYPE flag
• [x] travis: build dependencies with spack
• [x] component support: PARALLEL (as before), MPI, COLLECTIVE and TOOLS