fix: Keyboard accessible context menus (#1768)

- Makes menus fully accessible and keyboard driven
- Currently adds 2.8% to initial bundle size due to the inclusion of Reakit and its dependency, popperjs.
- Converts all menus to functional components
- Remove old custom menu system
- Various layout and flow improvements around the menus

closes #1766

app/scenes/Search/Search.js

@@ -361,6 +361,7 @@ class Search extends React.Component<Props> {
                     highlight={this.query}
                     context={result.context}
                     showCollection
+                    showTemplate
                   />
                 );
               })}