sweep: create sweep parameters struct

Prepares for adding more input-specific sweep parameters.

contractcourt/commit_sweep_resolver.go

@@ -206,7 +206,7 @@ func (c *commitSweepResolver) Resolve() (ContractResolver, error) {
 	c.log.Infof("sweeping commit output")
 
 	feePref := sweep.FeePreference{ConfTarget: commitOutputConfTarget}
-	resultChan, err := c.Sweeper.SweepInput(inp, feePref)
+	resultChan, err := c.Sweeper.SweepInput(inp, sweep.Params{Fee: feePref})
 	if err != nil {
 		c.log.Errorf("unable to sweep input: %v", err)