Rework badge counting

[Rayquaza01]

A user, Firefox user 57a3e1, has rated your addon, note-taker.

Rating: 4/5

You can view the rating here: 
https://addons.mozilla.org/addon/note-taker/reviews/1228372

Review Text:
Very interesting. I could suggest to add a notification badge if there is 
an URL note, so that it is visible (not only if ther is a Domain note)

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Currently, badges are counted from the note associated with the first tab of the default display.

This review asks for badges to display even if the current display does not have a note in the first tab or current display.

Examples that don't work now that will be addressed by this:

Display is domain.
No note on domain, note on URL.

Display is domain.
No note on tab 1, note on tab 2.