Merge pull request #16692 from owncloud/add_social_media_buttons

apps/files_sharing/css/3rdparty/gs-share/style.css

apps/files_sharing/css/settings-personal.css

apps/files_sharing/img/social-diaspora.svg

apps/files_sharing/img/social-facebook.svg

apps/files_sharing/img/social-gnu.svg

apps/files_sharing/img/social-googleplus.svg

apps/files_sharing/img/social-twitter.svg

apps/files_sharing/js/3rdparty/gs-share/gs-share.js

apps/files_sharing/js/settings-personal.js

apps/files_sharing/settings-personal.php

apps/files_sharing/templates/settings-personal.php