expanded unit test for CompositeVectorSource and caught a bug with the implementation of include_self
typo
- Changed vector_source from a constructor parameter to a train-time parameter for several pipeline estimators. This was it can be used as a resource and I get better control over when it is re-used or cloned.
 - Changed conf0 to include UnigramDummyComposer, which is required with vector-based vectorizers that use unigram features
- Added extra logging statements here and there.
Changed how things are parallelised- all folds of a classifier are done in parallel for a given data size instead of all data size at once,  but all folds serially. The concurrent processes should finish more or less simultaneously now, which might speed things up a bit.