blacklist failing/flawky integration tests
corrected typo
added some assertions and prepared custom kernels for quadratic time mmd
added constructor for using a custom kernel without features
updated unit test to use new constructor for custom kernel if no data is available
Merge pull request #957 from karlnapf/master

better handling for custom kernels for quadratic time mmd
added all three methods for null approximation to precomputed kernel test
Merge pull request #958 from karlnapf/master

extended test
make test scripts fail when a test fails
added a new kernel SSKStringKernel which implements the subsequence kernel (by lodhi et. al.). Also added to the modular interface
Added log_det method in CStatistics class
indentation fixed in Statistics.h
Fixed the previous messy commits