public static String createUniqueFilename(@NonNull final String requestedName, @NonNull final List<String> existingNames) {
        return createUniqueFilename(requestedName, existingNames, null);
    }
Create a unique non existing file named like the given file name. If a file with the given name already exists,
add a number as suffix to the file name.<br>
Example: For the file name "file.ext" this will return the first file of the list
<ul>
<li>file.ext</li>
<li>file_2.ext</li>
<li>file_3.ext</li>
</ul>
which does not yet exist.
main/src/main/java/cgeo/geocaching/utils/FileUtils.java