Mobile style for public links: files, folders, picture sets

Use with the mobile-style branch in core, see https://github.com/owncloud/core/pull/6777 cc @DeepDiver1975 @owncloud/designers 

To do:

* [x] change »Picture view« and »File list« to icons
* [x] change notice to »shared by username« as in Files

Anything else?