Add basic date filter

src/main/java/at/pcgamingfreaks/mkvaudiosubtitlechanger/config/validator/DateValidator.java

@@ -0,0 +1,22 @@
+package at.pcgamingfreaks.mkvaudiosubtitlechanger.config.validator;
+
+import at.pcgamingfreaks.mkvaudiosubtitlechanger.model.ConfigProperty;
+import at.pcgamingfreaks.mkvaudiosubtitlechanger.util.DateUtils;
+
+import java.util.Date;
+
+public class DateValidator extends ConfigValidator<Date> {
+    public DateValidator(ConfigProperty property, boolean required) {
+        super(property, required, null);
+    }
+
+    @Override
+    Date parse(String value) {
+        return DateUtils.convert(value); // TODO fix null return value
+    }
+
+    @Override
+    boolean isValid(Date result) {
+        return result != null;
+    }
+}