bkmartinjr/#294 rest sort (#300)

REST API now requires that the server sort all dataframe responses by dimension index (var or obs index), allowing the client (front-end) to assume responses will be sorted. Given that the dataframe usually has a natural ordering, and the server gets to arbitrarily assign indices, this is the most computationally efficient design.

This PR includes changes to the REST API spec, and removing the explicit sort in the front-end code.

client/src/util/stateManager/universe.js

@@ -116,7 +116,6 @@ function RESTv02AnnotationsResponseToInternal(response) {
   const keys = ["__index__", ...names];
   return _(data)
     .map(obs => _.zipObject(keys, obs))
-    .sortBy("__index__")
     .value();
 }