Citrix CTX1 Encoding/Decoding

[bwhitn]

This should add the requested operation for Citrix CTX1 encoded passwords in issue #413.

[n1474335]

Great work, thanks very much!

Just a few points to bear in mind in future:

• We prefer using Array.from to Buffer.from. Buffer is a Node type that doesn't exist in browsers. Babel will include a polyfill so that it works, but we'd rather use native JS code where possible. Array.from is ES6, so Babel will probably include a polyfill for it anyway, but we'd still rather use this syntax so that a polyfill is not required in future when support is broader.
• Make sure the operation class is named correctly. You had the operation named 'Citrix CTX1 Encode' and the class named EncodeCitrixCTX1. This seems like a small thing to worry about, but we do sometimes rely on the operation object having a predictable name so it's important we get it right. If you use the npm run newop helper script to create new operations, the names will all be generated for you correctly.
• When carrying out a validity check on the data, make sure you throw an OperationError when the check fails, rather than just returning a blank output. This makes it more clear to the user what has gone wrong and allows CyberChef to fail gracefully and predictably.

Nice work on the algorithm for this, I'm sure people will find it useful.