add geneset UI reducer

client/src/reducers/genesetsUI.js

@@ -0,0 +1,30 @@
+/*
+Reducers for geneset UI-state.
+*/
+const GeneSetsUI = (
+  state = {
+    createGenesetModeActive: false,
+    isEditingGenesetName: false,
+    genesetAddingNewGenes: null,
+  },
+  action
+) => {
+  switch (action.type) {
+    case "geneset: activate add new geneset mode": {
+      return {
+        ...state,
+        createGenesetModeActive: true,
+      };
+    }
+    case "geneset: disable create geneset mode": {
+      return {
+        ...state,
+        createGenesetModeActive: false,
+      };
+    }
+    default:
+      return state;
+  }
+};
+
+export default GeneSetsUI;