Parse/Validate rules when adding to a rule store

When using an instance of org.apache.stanbol.rules.manager.changes.AddRule to add a rule to a store, the rule is not parsed/validated. This means that any errors in the rule are not discovered until the recipe containing the rule is executed. It would be useful if rules were validated when they are added to the store. Currently we are using RuleParserImpl.parse(...) to check rules before adding them.