Add app utilities - CSS menus for sidebar

* has-menu, has-count
* use active for has-menu to show it
* use open for action popup to show up
* inactive buttons have less opacity
* borders for edit input
* use z-index for app content on mobile to prevent navigation items from sticking out
Merge pull request #10644 from owncloud/app-navigation-utils

Create boilerplate css code for navigation utilities, like delete and edit