Add "Favorite" action to the file actions menu

The new FileAction for the menu is essentially the same as the old
inline FileAction, except for the rendering; in this case the FileAction
is shown in the menu in a standard way, so there is no need to provide a
custom renderer (although the menu entry text and icon change depending
on whether the file is currently a favorite or not, but that can be done
just with displayName and iconClass functions).

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>