Use ES Class Fields & Static Properties (currently stage 2) for improve class outlook.

Added babel-plugin-transform-class-properties as a Babel plugin.

* 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