Turbo Render (#298)

* More responsive React updates on scroll

* `Icon`s now use shadow dom

* Faster Sparkline

* Recycle table rows

* Separate Header from Chain to avoid vdom diffing

* Separate THead from Row.HEADER to avoid vdom diffing

* Throttle rendering updates on chain tabs, also styles

* Minor tweaks and fixes

* Created components for all columns

* Wrapping up Column refactor

* Rename Row--td to Column

* Lazy `Ago`

* Update styles for faster layouting

* Minor cleanup

* Fix Connection

* Use shadow DOM in `PolkadotIcon`

* Comments and tweaks for the List component

* Faster Tooltip and Truncate

* Minor tweaks

* Tooltiped columns can now be copied

* Future-proof Connection

* Remove the <div> wrapper from Icon

* Fix dash on missing graph data

* Clean up some SVGs

* Cleanup and comments

* Localize the use of `previousKeys` to `recalculateKeys`

* Custom appState disjoint from React component state

* Make appState and appUpdate refs readonly

* Cleanup

frontend/src/components/List/Column/BlockPropagationColumn.tsx

@@ -0,0 +1,31 @@
+import * as React from 'react';
+import { Maybe } from '../../../common';
+import { Column } from './';
+import { Node } from '../../../state';
+import { milliOrSecond } from '../../../utils';
+import icon from '../../../icons/dashboard.svg';
+
+export class BlockPropagationColumn extends React.Component<Column.Props, {}> {
+  public static readonly label = 'Block Propagation Time';
+  public static readonly icon = icon;
+  public static readonly width = 58;
+  public static readonly setting = 'blockpropagation';
+  public static readonly sortBy = ({ propagationTime }: Node) =>
+    propagationTime == null ? Infinity : propagationTime;
+
+  private data: Maybe<number>;
+
+  public shouldComponentUpdate(nextProps: Column.Props) {
+    return this.data !== nextProps.node.propagationTime;
+  }
+
+  render() {
+    const { propagationTime } = this.props.node;
+    const print =
+      propagationTime == null ? '∞' : milliOrSecond(propagationTime);
+
+    this.data = propagationTime;
+
+    return <td className="Column">{print}</td>;
+  }
+}