systemctl: allow status with no units

This makes 'status' behave like 'list-units':
systemctl status -> status of all units
systemctl -t error status -> status of error units
systemctl -t mount status -> etc.
systemctl: Don't give re-activation warning if unit is masked
man: move bootchart README to manpage, docbooksify
bootchart: provide better error messages
bootchart: rename --filter to --no-filter

Turning off filtering with --filter is just too confusing.
Config option "Filter" doesn't have to be changed, here
"Filter=yes" already meant to filter.
man: prettify systemctl(1)

- reindent with two spaces, otherwise everything is squeezed near
  the right margin,
- mark only optional arguments as optional,
- some typos, etc.
systemctl: allow comma sepearted property lists