* Major update to life-preserver backend

Add new "automatic" mode for creating snapshots

When enabled, this will create snapshots in the following manner:

* Snapshots will be created every 5 minutes and kept for an hour.
* A hourly snapshot will be kept for a day.
* A daily snapshot will be kept for a month.
* A Monthly snapshot will be kept for a year.
* The life-preserver daemon will also keep track of the zpool disk space,
  if the capacity falls below 75%, the oldest snapshot will be auto-pruned.