Context menus for linking

[RangerMauve]

• Add to the context menu code
• Detect if the element that got right clicked has an id or it's direct parent.
• If there is no id, skip making this menu item
• If there is add a new menu item for "copy link to element" to the menu
• This should take the URL of the page and the element ID and copy a link to the fragmet

Similarly, we should detect if there is selected text and create + copy a link to the text fragment.

With this in place it should be way easier to link to sections of pages regardless of whether authors explicitly added anchors to those sections.

[RangerMauve]

Gonna skip the ID bit since the context menu event doesn't give us a sync method for getting the element id being clicked. Defs gonna do the fragment tho.