Show unread count in dropdown menu

[invalidCards]

I have 10 e-mail accounts linked to N1 and every time I get an e-mail I have to search through all my accounts until I find the one with the unread message. Adding an unread count to the dropdown menu (eg. instead of the avatar) or adding the e-mail address in the notification would help a lot with this.

[jstejada]

merging into #468