do not hard-wire column names in annotations (#785)

* enforce column name uniqueness for obs and var

* parameterize the column name containing obs and var user-readable names

* use the new annotation index value from schema

* update f/e unit tests

* PR review suggestions

* lint

client/__tests__/util/stateManager/universe.test.js

@@ -53,7 +53,7 @@ describe("createUniverseFromResponse", () => {
 
     expect(universe.obsAnnotations.dims).toEqual([
       nObs,
-      REST.schema.schema.annotations.obs.length
+      REST.schema.schema.annotations.obs.columns.length
     ]);
     expect(universe.obsLayout.dims).toEqual([nObs, 2]);
     expect(universe.obsLayout.colIndex.keys()).toEqual(
@@ -61,7 +61,7 @@ describe("createUniverseFromResponse", () => {
     );
     expect(universe.varAnnotations.dims).toEqual([
       nVar,
-      REST.schema.schema.annotations.var.length
+      REST.schema.schema.annotations.var.columns.length
     ]);
     expect(universe.varData.isEmpty()).toBeTruthy();
   });