Show boosted user's avatar (#2518)

* Show boosted user's avatar

* add .status__avatar-boost

* margin

* apply to notifications too.

* account__avatar-boost

* Add inline prop to Avatar component

* Add AvatarOverlay component

* rename mixins.scss

* move files for latest master

* fixed for webpack

app/javascript/styles/application.scss

@@ -1,3 +1,4 @@
+@import 'mixins';
 @import 'variables';
 @import 'fonts/roboto';
 @import 'fonts/roboto-mono';