Enhancement: OcTableFiles Contextmenu Tooltip 

Since most of the quickactions in the OcTableFiles have a tooltip the 
contextmenu button should get one, too. It also replaces the (removed) Showdetails 
button and leads to better discoverability of the contextmenu (and therefore the sidebar).

https://github.com/owncloud/owncloud-design-system/pull/1610
