[Scala] Allow for UUID types in akka-scala

[rmalleman]

PR checklist

• Read the contribution guidelines.
• Ran the shell/batch script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates)
• Filed the PR against the correct branch: master for non-breaking changes and 2.3.0 branch for breaking (non-backward compatible) changes.

Description of the PR

imported java.util.UUID in the model to allow for UUID types

[wing328]

@rmalleman thanks for the PR.

Starting from 2.3.0 (next major release), we'll consolidate scala and async-scala into a single scala generator via #4855. When you've time, please give it a try and let us know if you've any feedback.

Ideally we want to merge "akka-scala" into scala generator as an option/switch (e.g. --supportAkka). Please let us know if you've any feedback/concern on this.

(for your upcoming PRs, I would suggest you to create a new branch as per bit best practices)

[wing328]

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[rmalleman]

Consolidation sounds great, ill give that pr a go. Thanks for accepting.