Add update instructions to package.xml
Delete obsolete cache folder
Add gitignore
Show Dummy-App Logo in ACP
Adapt to latest WoltLab/WCF changes

See WoltLab/WCF@dcc2332d
Adapt to other WoltLab/WCF merges too

WoltLab/WCF@
WoltLab/WCF@
WoltLab/WCF@