Mark `PagerankTable` components as pure (#485)

Summary:
As we add sliders for adjusting the PageRank parameters, we trigger a
bunch of unneeded renders on `PagerankTable`. As `PagerankTable` is a
pure component, we can [mark it and its children as such][1] to see notable
performance improvements: the `Array.from` and `sort` in its `render`
method are showing up on the flamegraph.

[1]: https://reactjs.org/docs/react-api.html#reactpurecomponent

Paired with @decentralion.

Test Plan:
Unit tests pass, whereas if we instead implement `shouldComponentUpdate`
by `return false` then the interaction tests fail. Also, `yarn start`
seems to behave as expected as we switch among different graphs.

wchargin-branch: pure-pageranktable

src/app/credExplorer/PagerankTable.js

@@ -48,7 +48,7 @@ export function nodeDescription(
   }
 }
 
-export class PagerankTable extends React.Component<Props, State> {
+export class PagerankTable extends React.PureComponent<Props, State> {
   constructor() {
     super();
     this.state = {topLevelFilter: NodeAddress.empty};
@@ -152,7 +152,7 @@ type RTProps = {|
   +adapters: $ReadOnlyArray<PluginAdapter>,
 |};
 
-class RecursiveTable extends React.Component<RTProps, RTState> {
+class RecursiveTable extends React.PureComponent<RTProps, RTState> {
   constructor() {
     super();
     this.state = {expanded: false};
@@ -221,7 +221,7 @@ type RecursiveTablesProps = {|
   +adapters: $ReadOnlyArray<PluginAdapter>,
 |};
 
-class RecursiveTables extends React.Component<RecursiveTablesProps> {
+class RecursiveTables extends React.PureComponent<RecursiveTablesProps> {
   render() {
     const {addresses, graph, pagerankResult, depth, adapters} = this.props;
     return addresses