unify export filename logic

src/main/java/de/dennisguse/opentracks/io/file/ExportFileName.java

@@ -0,0 +1,10 @@
+package de.dennisguse.opentracks.io.file;
+
+import de.dennisguse.opentracks.content.data.Track;
+
+public class ExportFileName {
+
+    public static String getExportFileNameByTrackId(Track.Id trackId, String trackFileFormatExtension) {
+        return trackId.getId() + "." + trackFileFormatExtension;
+    }
+}