B&R: Add QDir::homePath() to newly created Tartget-Sets

Kåre Särsrequested to merge
work/sars/improve_default_build_commands into master

There has been a bunch of confusion on how to use the build plugin. Especially on how to set the working directory. Add the home directory as a placeholder so that it is easier to understand.

At the same time remove the "Config Clean" target and use Ninja

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