Added sc_mutex.h to src/clutils

It is wrapper to std::mutex. It does nothing if HAVE_STD_MUTEX is not defined.
Added a test for checking thread safety in instmgr

The test tries to insert and delete instances simultaneosly, sequentially and parallely and later compares there results for any disparity.
Modified CMakeLists.txt to include HAVE_STD_THREAD defs.

The cmake files of cldai, cleditor & clstepcore libraries have been changed.
Removed duplicate code
Made Append / Delete in instmgr thread safe.

The InstMgr_thread_safety_test passes. Had to a change file in cmake directory in order to compile the changes.