Transaction confirmations: fork edit to edit_before and edit_after

edit_before confirms the change of attributes that have been already
altered in the database. Therefore it does nothing if the transaction
succeeds and reverts the original value if it fails.

edit_after is an alias to the original edit and works exactly
the other way around - changes attributes on success, nothing
if failed.
New way of transactional updating VPS properties

Attributes are changed using the edit_after confirmations. Method
attributes which need to be changed via transaction and creates
transaction chain VpsUpdate if necessary. The chain contains
transactions changing the attributes.

Remaining attributes are saved immediately, just as implicit #update
does.
Transaction chain: rollback if the chain is empty