Incorporate sleep.conf into logind.conf

Incorporate sleep.conf into logind.conf

* src/login/logind-action.c (shutdown_or_sleep, do_sleep): Take modes
  from the manager instead of parsing them ourselves.

* src/login/logind-dbus.c (execute_shutdown_or_sleep): Adapt to
  shutdown_or_sleep prototype change.

* src/login/logind-gperf.gperf: Add config items from sleep.conf.
* src/login/logind.c (manager_new): Wire up defaults for new config
  items.
  (manager_free): Free new config items.
  (manager_parse_config_file): Arrange to parse a single
  elogind/logind.conf file, not grovelling all over the filesystem.
  Take the file from the ELOGIND_CONF_FILE environment variable if
  present.