Refs #8508 Moved to a C++ algorithm

modified:   Framework/CurveFitting/CMakeLists.txt
new file:   Framework/CurveFitting/inc/MantidCurveFitting/DiffRotDiscreteCircle.h
new file:   Framework/CurveFitting/src/DiffRotDiscreteCircle.cpp
new file:   Framework/CurveFitting/test/DiffRotDiscreteCircleTest.h
deleted:    Framework/PythonInterface/plugins/functions/DiffRotDiscreteCircle.py