Insert block menu (#297)

* Insert block behavior

* Functional with horizontal rule

* Add list and image upload working

* Cleanup typing

* Closest to correct behavior so far

* Improve block insert on list

* Hide (+) after clicking menu item

* Bad merge

frontend/components/DropdownMenu/DropdownMenuItem.js

@@ -7,7 +7,7 @@ const DropdownMenuItem = ({
   onClick,
   children,
 }: {
-  onClick?: () => void,
+  onClick?: SyntheticEvent => void,
   children?: React.Element<any>,
 }) => {
   return (
@@ -24,11 +24,15 @@ const MenuItem = styled.div`
 
   color: ${color.slateDark};
   display: flex;
-  justify-content: space-between;
+  justify-content: left;
   align-items: center;
   cursor: pointer;
   font-size: 15px;
 
+  svg {
+    margin-right: 8px;
+  }
+
   a {
     text-decoration: none;
     width: 100%;