Expose lineage trace for python-systemDS

[phaniarnab]

This patch contains the implementation of exposing lineage trace to python users. Lineage trace can be retrieved by one of the below ways: 1) by passing a lineage = True to compute() function

print(m_sum.compute(verbose = True, lineage = True))

2) by calling getLineageTrace() on any intermediate.

print(m_res.getLineageTrace())

Note: Unit test setup is not ready yet but the reviewer can execute test_lineage.py and test_l2svm_lineage.py files to display lineage trace.