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/components/DocumentHistory/components/Revision.js

@@ -1,6 +1,5 @@
 // @flow
 import format from "date-fns/format";
-import { MoreIcon } from "outline-icons";
 import * as React from "react";
 import { NavLink } from "react-router-dom";
 import styled, { withTheme } from "styled-components";
@@ -45,9 +44,7 @@ class RevisionListItem extends React.Component<Props> {
           <StyledRevisionMenu
             document={document}
             revision={revision}
-            label={
-              <MoreIcon color={selected ? theme.white : theme.textTertiary} />
-            }
+            iconColor={selected ? theme.white : theme.textTertiary}
           />
         )}
       </StyledNavLink>