Enhancement: Redesign Filetype icons

We've adjusted the resource icons to fit the redesign.
We've added a new OcResourceIcon component that is themable.

https://github.com/owncloud/web/issues/6278
https://github.com/owncloud/owncloud-design-system/pull/1900
https://github.com/owncloud/owncloud-design-system/pull/1924
https://github.com/owncloud/owncloud-design-system/pull/1925
https://github.com/owncloud/owncloud-design-system/pull/1934
