Add a message segment to the Account CDA

[kwek20]

Description

A message is often required, if we have a standard way of creating this for everyone, mistakes are less likely to happen. The length of the message depends on the CDA delivery method. a QR is only of limiting size, whilest a magnet link can be as big as you want. If the method does not support the length, we will throw an error (InvalidParameterException)

Motivation

We want users to be able to include a message to their CDA link/QR

Requirements

• Add message to the CDA class
• Allow construct/deconstruct of message segment in the DepositMethod child classes
• Update the tests according to these classses