Handle multiple bookmarks on popup

[peterhil]

This enables saving multiple bookmarks or editing multiple existing bookmarks from the popup.
Get the selected tabs with query: {currentWindow: true, highlighted: true}.

Ideas:

• Move category on top then group URL and title, with URL being before title – this has the advantage of having category search on top, which can be used for searching existing bookmarks and showing the results below
• Enable bookmarking selected or all tabs on window at once
• Maybe implement carousel UI element for multiple bookmark results or just list the bookmarks with URL and titles grouped?
• When there are multiple bookmarks for an URL: show the URL only once and list individual bookmarks with title (and maybe parent category), but enable deleting, moving and editing each bookmark using buttons or some dropdown