[ENH] Corpus & Bow: Improve sparsity handling according to Orange>=3.8.0#281

Merged

nikicc merged 1 commit intobiolab:masterfrom nikicc:sparsity-fixups

Dec 5, 2017

+8-8

Commits on Dec 4, 2017

Corpus & Bow: Improve sparsity handling as of Orange 3.8
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