Fix sorting&paging on RDBMS store

compose/types/attachment.go

@@ -36,8 +36,6 @@ type (
 		FieldName   string `json:"fieldName,omitempty"`
 		Filter      string `json:"filter"`
 
-		Sort string `json:"sort"`
-
 		// Check fn is called by store backend for each resource found function can
 		// modify the resource and return false if store should not return it
 		//
@@ -45,6 +43,7 @@ type (
 		Check func(*Attachment) (bool, error)
 
 		// Standard helpers for paging and sorting
+		filter.Sorting
 		filter.Paging
 	}