Create public functions to update the kinematics based on one invariant mass and the corresponding helicity angle close #55. Fixing a bug in one of the protected functions that was not actually used. Commit also the test code to a new test directory.

git-svn-id: svn+ssh://phab.hepforge.org/source/laurasvn/trunk@398 30227d83-a2f9-49e9-9e98-657c83b2c86a