Add basic date filter

src/main/java/at/pcgamingfreaks/mkvaudiosubtitlechanger/util/DateUtils.java

@@ -0,0 +1,25 @@
+package at.pcgamingfreaks.mkvaudiosubtitlechanger.util;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+
+public class DateUtils {
+    private static final SimpleDateFormat dateFormat = new SimpleDateFormat("dd.MM.yyyy-HH:mm:ss");
+
+    public static Date convert(long millis) {
+        return new Date(millis);
+    }
+
+    /**
+     * Convert String to date.
+     * @return parsed date, null if exception occurs
+     */
+    public static Date convert(String date) {
+        try {
+            return dateFormat.parse(date);
+        } catch (ParseException e) {
+            return null;
+        }
+    }
+}