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cells (universe), the differential expression results are no longer
valid.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/__tests__/e2e/e2eAnnotations.test.js

@@ -22,22 +22,6 @@ describe.each([
   {withSubset: false, tag: "whole"}
 ])("annotations", (config) => {
 
-  async function subset() {
-    const lassoSelection = await cxgActions.calcDragCoordinates(
-      "layout-graph",
-      {x1: 0.10, y1: 0.10, x2: 0.80, y2: 0.80}
-    );
-    await cxgActions.drag(
-      "layout-graph",
-      lassoSelection.start,
-      lassoSelection.end,
-      true
-    );
-    await utils.clickOn("subset-button");
-    const coordinate = await cxgActions.calcCoordinate("layout-graph", 0.9, 0.9);
-    await cxgActions.clickOnCoordinate("layout-graph", coordinate);
-  }
-
   const perTestCategoryName = "per-test-category";
   const perTestLabelName = "per-test-label";
 
@@ -48,7 +32,7 @@ describe.each([
     // setup the test fixtures
     await cxgActions.createCategory(perTestCategoryName);
     await cxgActions.createLabel(perTestCategoryName, perTestLabelName);
-    if (config.withSubset) await subset();
+    if (config.withSubset) await cxgActions.subset({x1: 0.10, y1: 0.10, x2: 0.80, y2: 0.80});
     await utils.waitByClass("autosave-complete");
   });