Merge remote-tracking branch 'origin/6.0'

Merge remote-tracking branch 'origin/6.0'

# Conflicts:
#	com.woltlab.wcf/package.xml
#	syncTemplates.json
#	wcfsetup/install/files/js/WoltLabSuite.Core.min.js
#	wcfsetup/install/files/lib/action/FacebookAuthAction.class.php
#	wcfsetup/install/files/lib/action/GithubAuthAction.class.php
#	wcfsetup/install/files/lib/action/GoogleAuthAction.class.php
#	wcfsetup/install/files/lib/action/TwitterAuthAction.class.php
#	wcfsetup/install/files/lib/system/WCF.class.php
#	wcfsetup/install/files/lib/system/html/node/HtmlNodeUnfurlLink.class.php
#	wcfsetup/install/lang/de.xml
#	wcfsetup/install/lang/en.xml