[WIP] [Ticket/12888]

####TODOs:
-[] Fix target unread & latest unread
-[] Finalize icons
-[] Cleanup deprecated code

####Compatability
-[] Safari
-[x] Chrome
-[] Firefox
-[] IE All
-[] IOS
-[] Android All

PSD: https://www.dropbox.com/s/6awigiemq4kv10q/navigation-icons.psd
Ticket: https://tracker.phpbb.com/browse/PHPBB3-12888

PHPBB3-12888