load annotations incrementally (#1107)

* load annotations individually

* fix type check to be more general

* update node CI version from 10 to 12

* node 11

* debug print node version

* travis node version to latest

* try nvm

* remove extraneous node_js statement

* remove node version debugging printf

* incrementally load all annotations and layout

* process annotations and layout as they are loaded

* fix tests

* sort categories incrementally

* incrementally build category view summary; add category loading spinner

* add spinner to continuous metadata

* configure undoable reducer

* incremental crossfilter creation

* improve busy layout

* more layout cleanup

* correctly reconcile categories in schema

* refine layout of lsb spinners

* more spinner layout work

* more spinner layout

* always load layout before obs annotations

client/src/components/graph/graph.js

@@ -255,7 +255,7 @@ class Graph extends React.Component {
     const { regl, toolSVG, camera, modelTF } = this.state;
     let stateChanges = {};
 
-    if (regl && world) {
+    if (regl && world && crossfilter) {
       /* update the regl and point rendering state */
       const { obsLayout, nObs } = world;
       const { drawPoints, pointBuffer, colorBuffer, flagBuffer } = this.state;