Bookmarks toolbar: open link in new window

[cndouglas]

Test Plan:

#8218 (comment)

1. If there is not an item in the bookmarks toolbar, add one with Bookmark Page.
2. Right-click the bookmark and click Open Link in New Window.
3. Make sure the bookmarked page opens in a new window.

Original issue description

• Did you search for similar issues before submitting this one?
  Yes.

• Describe the suggestion:
  "Open Link in New Window" should be an option for items in the bookmarks toolbar.

• Current behavior:
  As of 0.14.1, there is no such option:
  

• Extra QA steps:

  1. If there is not an item in the bookmarks toolbar, add one with Bookmark Page.
  2. Right-click the bookmark and click Open Link in New Window.
  3. Make sure the bookmarked page opens in a new window.

• Screenshot if needed:
  Example from Can't have two instances at the same time #8019 (comment) (Firefox):
  

• Any related issues:
  None.