fix: Add access to document TOC on mobile (#2279)

* Add TOC button for mobile

* Undo NewDocumentMenu changes

* Place the toc button in the correct position.

* Pass menu props to menuitem

* Update app/menus/TableOfContentsMenu.js

Co-authored-by: Tom Moor <tom.moor@gmail.com>

* Update app/menus/TableOfContentsMenu.js

Co-authored-by: Tom Moor <tom.moor@gmail.com>

* Use the existing prop type

* Write menu inside actions prop

* Prevent blank webpage behaviour for toc

* Use href instead of level to determine target

* Update app/scenes/Document/components/Header.js

Co-authored-by: Tom Moor <tom.moor@gmail.com>

* Add heading to menu items

* Use existing Heading component

Co-authored-by: Tom Moor <tom.moor@gmail.com>

app/scenes/Document/components/Document.js

@@ -374,6 +374,7 @@ class DocumentScene extends React.Component<Props> {
               sharedTree={this.props.sharedTree}
               goBack={this.goBack}
               onSave={this.onSave}
+              headings={headings}
             />
             <MaxWidth
               archived={document.isArchived}