Refactor code for task-specific browsers

The code in config/chroot_local-includes/usr/local/sbin/unsafe-browser should be refactored into a shell (or whatever) library. Code-sharing would be useful for the Unsage Browser and #7725 (closed) and other task-specific browsers (LAN browser?).

Feature Branch: bugfix/7951-refactor-chroot-browsers

Related issues

Related to #7725 (closed)
Related to #7976 (closed)
Blocks #7419 (closed)

Original created by @anonym on 7951 (Redmine)

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