We don't need two (and half) templating systems anymore, yay!
I'm keeping the changes minimal, to make the diff manageable. Some enhancements
due to a better templating system might be possible in the future.
For handling of '## ' — see the next commit.
This is might be useful in some cases, but it's primarily an example for
a boot check service that can be plugged before boot-complete.target.
It's disabled by default.
All it does is check whether the failed unit count is zero
