last kernel selection strategy and bugfixes

We now have:
max mmd single kernel (linear and quadratic time mmd)
optimal single kernel (linear time mmd)
max mmd L2 combined kernels (linear and quadratic time mmd)
optimal combined kernel (linear time mmd)
The linear time MMD cases all work with streaming data, also the combined case where the covariance matrix Q is computed in an online fashion.

All methods come with tests and a very flexible framework, easy to extend etc
What is missing is python examples, doxygen documentation, and tutorial update