Move spring-shell-samples to a separate repository

[piotrooo]

To keep the project codebase clean, I propose moving the samples to a separate repository — just like we do in other projects:

• https://github.com/spring-projects/spring-security-samples
• https://github.com/spring-projects/spring-amqp-samples
• https://github.com/spring-projects/spring-data-examples

[fmbenhassine]

Unfortunately we have no bandwidth to manage samples in a different repos for now..

Thank you for the suggestion anyway.