fs: deglobalise the config #4685

This is done by making fs.Config private and attaching it to the
context instead.

The Config should be obtained with fs.GetConfig and fs.AddConfig
should be used to get a new mutable config that can be changed.

fs/accounting/inprogress.go

@@ -15,8 +15,9 @@ type inProgress struct {
 
 // newInProgress makes a new inProgress object
 func newInProgress(ctx context.Context) *inProgress {
+	ci := fs.GetConfig(ctx)
 	return &inProgress{
-		m: make(map[string]*Account, fs.Config.Transfers),
+		m: make(map[string]*Account, ci.Transfers),
 	}
 }