Ctest configuration

This replicates issue #115 (closed) , which in turn traces back to !103 (merged), regarding ctest and gtest.

I finally left the project as this (checkout branch frame-base-tests):

• wolf/src/tests --> here all the gtest files are located

• In wolf/CMakeLists.txt

if(BUILD_TESTS)
    enable_testing()
endif()

• In wolf/src/CMakeLists.txt

if(BUILD_TESTS)    
    MESSAGE("Building tests.")
    add_subdirectory(test)
endif()