Integrate config/use_local_mirror

--

Commit: config@fe6da031

setup:script: Optionally replace global downloads with mirror

Add option to use the global download directory as local mirror instead
of as actual download directory.
This option is a "cleaner" approach of sharing the download state
between multiple users on the same system.
Sharing the same folder directly often led to permission issues in the
past.

--

Commit: config@42318a78

Revert "setup:script: Add optional download mirror for Yocto"

This reverts commit f4485d8d6e789ce20da077732883cca79a607a9f.