Support n_jobs, other changes

[bibikar]

@oleksandr-pavlyk

This quick PR addresses the following

• Allow n_jobs in sklearn and only use it if daal is not present
• Makefile: use rbf kernel for SVM by default
• Use LinearSVC when not using daal and linear kernel is selected in SVM (#14)
• specify OMP_NUM_THREADS in Makefile when single-threaded execution is specified, so stock benchmarks will not be implicitly threaded while we want them to run serially.
• specify USE_DAAL4PY_SKLEARN = yes in makefile so daal will be used when needed
• decrease SVM problem size