* move the chat unread indicator to top to match the profile avatar indicator
* add white border to profile avatar indicator (badge notification) to match chat indicator and userstatus styling
* change `.urgent` to BEM
* congregate all styling into mixin
* update chat index to use mixin
* update thread indicator to use mixin
* update header indicator to use mixin
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Co-authored-by: Joffrey JAFFEUX <j.jaffeux@gmail.com>
Co-authored-by: Martin Brennan <martin@discourse.org>
