Transaction chain: use_in arguments in args

Arguments to included chains are now passed in a named argument
called 'args'. This will allow passing more options to the included
chain, for example urgency, priority.
Support urgent transactions/chains

TransactionChain#use_chain and #append now accept boolean named argument
'urgent', by which it is possible to set urgency to whole chain
or a specific transaction.
VPS migration: use urgent transactions
Transaction rollback and reversibility flag
Mark destroy transaction as irreversable
Vps::IpDel: send params required for rollback
Shaper::Unset: send params required for rollback