Added CMakeLists.txt for Cereal.

Despite the apparent huge diff, I suspect this is once again git's line-ending randomiser at play.

The only deliberate change I made with regards to the Cereal files was to move them all into a new folder /include/cereal (to avoid having to add the third_party_libs folder as a compiler search path), and to add a couple of MSVC pragmas in https://github.com/Fraser999/MaidSafe/compare/MAID-59_cereal_cmake?expand=1#diff-16 to disable an MSVC warning.