Change icon bubble colour logic

[marcosmenendez]

The bubble that shows the number of threats detected below the icon should work in this way:

• In case that more than 50% of them are allowed, the bubble should be green (same green as the one showed in the "allowed" button in the extension)
• If 50% or less of the extensions are allowed, this button should be red (same red as the one showed in the "blocked" button)