Merge pull request #849 from karlnapf/master

MMD kernel selection work
refactored existing combined kernel selection classes a bit to make ground for a new class. Now got a base class which solves the optimisation problem for a given Q matrix and MMDs vector
typo correction
fixed virtual method call crashes
fixed a memory leak due to static context SGReferenced
added new kernel selection strategy: max mmd l2 norm regularized convex conbination. works
added test for max mmd l2 kernel selection
fix memory bugs/leaks caused by SGReferenced and static context. Do everything by hand now. Works now in valgrind tests