Don't remove genes from workspace upon reset

cc @aopisco “STOP LOSING THE GENE LIST IF I RESET” (currently using ‘undo undo undo’ to get back to universe instead of using reset because of this)

This is consistent with the proposed gene sets work in #1069

[mweiden]

To summarize the desired behavior as I understand it:

1. If you add a gene and then press “Undo” that removes the gene. If you then press “Redo” the gene is added back.
2. If you add a gene and then press “Reset,” the gene is not removed.

Notice that both mirror the undo/redo/reset behavior of adding a category on the left-hand side.

[colinmegill]

I’m fine with not clearing diffexp as a stopgap