units: reorder/split unit dependency blocks

units: reorder/split unit dependency blocks

The block is reordered and split to have:
  1. description + documentation
  2. (optionally) conditions
  3. all the dependencies
I think it's easier to read the units this way.
Also, the Conflicts+Before is seperated out to separate lines.
The ordering dependency is "fake", because it could just as well be
After=, we are adding it to force ordering wrt. shutdown.target, and
it plays a different role than the other Before=, which are about a
real ordering on boot.