Bugfix: Removed width class from sidebar menu

There were different values for width of the sidebar menu and it's left position when hidden.
We've removed the width class so that the width and left position are the same and the sidebar menu is no more overlapping when it's state is hidden.

https://github.com/owncloud/owncloud-design-system/issues/668
https://github.com/owncloud/owncloud-design-system/pull/669
