Add support for bootacl

Closes #77 (closed)

Quick summary of the implementation:

• domains are now persistent
  • new Uid (dbus) / uid (object) property derived from the uuid of the device representing the root switch
  • sysfs and id attribute will be set/unset on connects and disconnects
  • domains are now stored
• domains got the BootACL (dbus) / bootacl (object) property
  • uuids can be added, removed or set in batch
  • when domain is online: changes are written to the sysfs boot_acl attribute directly
  • when domain is offline: changes are written to a journal and then reapplied in order when the domain is connected
• newly enrolled devices get added to all bootacls of all domains if the policy is BOLT_POLICY_AUTO
• removed devices get deleted from all bootacls of all domains
• boltacl domain command will show the bootacl slots and their content