refactored systemd unit API to allow specifying non-primary section settings
systemd: extended docs
fixed bugs in systemd unit generation, made some exported symbols internal
added systemd integration tests (requires manual setup, so disabled by default for now)
additional systemd fixes & tests
clean up systemd docs
systemd: additional error handling and added changelog details
update sjs
updated changelog
doc: allow page to override the defult hubs
parse X-Conductance-Group setting to deal with ambiguous unit names

Also added uninstall --all, to uninstall all conductance-installed units
(regardless of group)
add systemd list --all option
Merge branch 'systemd-refactor'