Add basic multi-select support (no actions, nothing in right pane)

Author: pimterry

src/components/view/multi-selection-summary-pane.tsx

@@ -0,0 +1,16 @@
+import * as React from 'react';
+import { observer } from 'mobx-react';
+
+import { CollectedEvent } from '../../types';
+
+import { EmptyState } from '../common/empty-state';
+
+export const MultiSelectionSummaryPane = observer((props: {
+    selectedEvents: ReadonlyArray<CollectedEvent>
+}) => {
+    const count = props.selectedEvents.length;
+
+    return <EmptyState icon='ListChecks'>
+        {count} event{count !== 1 ? 's' : ''} selected
+    </EmptyState>;
+});