Refactor: Add Validator flag to Check

Checkable now checks if an accepted Visitor is flagged as a Validator
before setting the object as validated=true. Allows the implementation
of Visitors for the Check-Engine that serve as utilities, e.g. to enable
decoupled collection of all contained Geometries in a CityObject.

CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/check/Check.java

@@ -53,6 +53,7 @@ public abstract class Check {
 
 	private final List<Class<Checkable>> applicableToClasses = new ArrayList<>(2);
 
+
 	@SuppressWarnings("unchecked")
 	protected Check() {
 		Method[] declaredMethods = getClass().getDeclaredMethods();
@@ -102,6 +103,15 @@ public abstract class Check {
 	 */
 	public abstract RequirementType getType();
 
+	/**
+	 * Returns whether this check validates a feature.
+	 *
+	 * @return true if it validates, false otherwise
+	 */
+	public boolean isValidator() {
+		return true;
+	}
+
 	/**
 	 * Checks whether the check can be executed on this checkable, meaning the
 	 * checkable or its content can not have any error of any check dependent on

CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/check/Checkable.java

@@ -71,7 +71,9 @@ public abstract class Checkable implements Serializable {
 		if (c.canExecute(this)) {
 			c.check(this);
 		}
-		setValidated(true);
+		if (c.isValidator()) {
+			setValidated(true);
+		}
 	}
 
 	/**