Fix style of "coz-bar-container"

[Merkur39]

I notice that at least in Drive and in Mes papiers, we overload this style

cozy-bar/src/styles/bar.css

Line 38 in 8f4e374

padding: 0 1em 0 0;

Otherwise the icon is not aligned with the rest of the icons in the application.
For Drive: https://github.com/cozy/cozy-drive/blob/master/src/components/Button/index.styl#L16
For Mes papiers: cozy/mespapiers@7e0ca96

It would be possible to replace this rule by padding: 0 ?