Offer set analysis across datasets

[AlexanderPico]

If more than one dataset in run, then add top-level drop-down in Results tab to "Compare with..." another dataset result, plus another drop-down for "Union" or "Difference" (A vs B; offer icon to swap set order).

• Changes table (per db) to a union or setdiff listing with A/B geneLists. Display concatenated stats or new stats about intersection?
• Plot1 remains the same, plus add a new heatmap: datasets (row) vs top n union terms (columns) [maybe always include this plot for all datasets when more the one? And limit to A/B pair iff "Compare with..."?]
• Plot2 remains the same, with diff (A) genes highlighted or with 3-color code for A/B/union genes