Undo selection appends genes from differential expression to user gene list (#1183)

* Undo selection appends diffExp genes to user gene list

Fixes https://github.com/chanzuckerberg/cellxgene/issues/1171

Need: When a user performs a differential expression from within
a sub-selection (world) of the data and then resets the selection to all
cells (universe), the differential expression results are no longer
valid.

Approach:
* When the selection is reset, move the top (maxUserDefinedGenes
- len(userDefinedGenes) from the differential expression results to the
list of user defined genes
* Raise maxUserDefinedGenes to 25 to give users more room and
accommodate the extra genes transferred in from differential expression

Other commits:
* Choose different button icons
* Add diff exp genes to user defined genes on subset too
* Respond to feedback from @liaprins-czi and @bkmartinjr

client/src/reducers/undoableConfig.js

@@ -16,7 +16,6 @@ const skipOnActions = new Set([
   "configuration load complete",
   "increment graph render counter",
   "window resize",
-  "user reset start",
   "reset colorscale",
   "reset centroid labels",
 
@@ -65,7 +64,6 @@ const clearOnActions = new Set([
   "initial data load complete (universe exists)",
   "reset World to eq Universe",
   "initial data load error",
-  "user reset end"
 ]);
 
 /*