policy-dl: Minor schema update

Author: kostyantynv

rsvp/policy-ast/src/main/java/uq/pac/rsvp/policy/ast/schema/Schema.java

@@ -300,4 +300,11 @@ public Schema resolveCommonTypes() {
         }
         return new Schema(resolved);
     }
+
+    /**
+     * Return {@code true} if this schema has no unresolved types
+     */
+    public boolean isResolved() {
+        return types().findAny().isEmpty();
+    }
 }