When creating an escrow, if the `CancelAfter` time is specified but
the `FinishAfter` is not, the resulting escrow can be immediately
completed using `EscrowFinish`. While this behavior is documented,
it is unintuitive and can be confusing for users.
This commit introduces a new fix amendment (fix1571) which prevents
the creation of new Escrow entries that can be finished immediately
and without any requirements.
Once the amendment is activated, creating a new Escrow will require
specifying the `FinishAfter` time explicitly or requires that a
cryptocondition be specified.