Link context menu should display shortcuts

[irgolic]

Now that link selection (#114) is a thing, and context menu shortcuts (#136) are a thing, the link's context menu should also show shortcuts. E.g., remove should show the backspace icon, as it does in the widget's context menu.

This is a matter of refactoring I think, with which some other nuances will be taken care of. For example, selecting some widgets and a link, then right-clicking the link shouldn't clear the selection, it should behave the same way as right-clicking a widget does.