Decode up to 2 times with `extract-base64`

[YamatoSecurity]

It would be nice to decode up to the second encoded Base64 string with the extract-base64 command.
So change Decoded String column to First Decoded String and add a Second Decoded String column to the right of it. It will usually be blank unless there is another embedded encoded string.
We do not need to add columns to detect if the second encoded string is binary, its length, encoding etc...

If the second encoded string is binary data, we should output <BINARY> though.

@fukusuket Would this be difficult to implement?

[fukusuket]

Sounds good! It seems a little difficult, but I will look into!💪