Design fixes

This supersedes https://github.com/owncloud/core/pull/4878 and https://github.com/owncloud/core/pull/4819

* fix disabled buttons not showing icons @Raydiation this fixes the import/export in news
* prevent hover effect when settings are open @Raydiation 
* increase font size of file actions for better readability
* add useful icon from News app to core cc @Raydiation (the toggle eye is already in core, grey colors are achieved via opacity)

@PVince81 @kabum @Kondou-ger please also review. :)