NIAD-2922: refactoring to add interfaces

[ole4ryb]

What

Interfaces were introduced into RCMR_IN030000UK06-related message objects

Why

In order to fully accommodate the new RCMR_IN030000UK07 message type interfaces should be introduced to make code more flexible. Also, introducing interfaces follows the best code practises.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Internal change (non-breaking change with no effect on the functionality affecting end users)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have performed a self-review of my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have updated the Changelog with details of my change in the UNRELEASED section if this change will affect end users
• A corresponding change has been made to the Mapping Documentation repository