Follow XDG base directory specifications

[FriedrichFroebel]

The application does not follow the XDG base directory specifications for now, as it saves its cache inside $HOME/.cmanager/cache. Correct would be $HOME/.cache/cmanager.

The old cache should probably be migrated, while deleting the old directory afterwards.

Specifications

• https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
• https://wiki.archlinux.org/title/XDG_Base_Directory

Possible implementations

• https://github.com/dirs-dev/directories-jvm: Maintained, but with Windows issues due to using a PowerShell script there. As far as I am aware, our user-base is mostly using Windows.
• https://github.com/omajid/xdg-java: No recent commits, but most basic implementation without using PowerShell scripts.