This commit splits out the parameters that shape the justice transaction
into their own struct, which then embedded within the overarching
wtpolicy.Policy which may have additional parameters describing
operation of the session.
This is done as a preliminary step to support comparison of sessions
based on matching TxPolicy configurations. This prevents otherwise
identical Policies from being counted as different if operational
parameters like MaxUpdates differ, even if it has no material difference
to the justice transaction.
This commit changes when the sweep pkscript
is assigned in the construction of the justice
transaction. Currently, the sweep pkscript is
assigned when the task is bound to a session.
However, we will moving to an assignment where
a unique sweep pkscript is used per channel to
prevent address inflation. Hence, this commit
makes the sweep pkscript a state dependent
variable, since it can be known at the time the
channel id is assigned.
