Support delayed load of services from plugins and bundled services

This adds a new function conf_save_service() replacing service_register() for
plugins and bundled services like watchdogd, keventd, runparts, etc.

The benefits to this change are several:

 - Plugin/Bundled services no longer risk starting before udev or other
   critical services/task have started
 - Definitions can be overridden by an administrator (see docs)
 - Increases visibility (user: where are all these services coming from?)
   Previously the origin (file the service was loaded from) was NULL.
 - Adds another level of extensibility to Finit

The most notable change is that dbus is no longer started before udevd.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/conf.h

@@ -45,6 +45,7 @@ int  conf_monitor         (void);
 void conf_reset_env       (void);
 void conf_saverc          (void);
 void conf_save_exec_order (svc_t *svc, char *cmdline, int result);
+void conf_save_service    (int type, char *cfg, char *file);
 void conf_parse_cmdline   (int argc, char *argv[]);
 int  conf_parse_runlevels (char *runlevels);
 void conf_parse_cond      (svc_t *svc, char *cond);