first draft of cmake build scripts

available cmake variables:
  pfasst_BUILD_TESTS={ON,OFF}
    enable build of tests with automatically pulling in GoogleMock and
    GoogleTest (both version 1.7.0), building and linking it; no need
    for them to be preinstalled

what it also provides:
  - auto-detecting C++11 compiler flags for GCC and Clang

what it (yet) not provides:
  - handling of XL/C++ compiler