Atrium: Iterable.containsNoDuplicates

[robstoll]

Platform (jvm, jdk8, js, android):

Code related feature

expect(iterable).containsNoDuplicates()

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Please react with :+1: if you would like to see this feature implemented in Atrium, the more upvotes the more likely I will implement it myself -- feel free to sponsor me, that would be a motivation too.
You are of course welcome to work on this issue. Write I'll work on it as comment so that we can assign the task to you.

[frikit]

I'll work on it

[robstoll]

@frikit as this is your first contribution, I advise:

• See Your first code contribution for guidelines.
• Do not hesitate to ask questions here or to contact us via Atrium's slack channel if you need help
  (Invite yourself in case you do not have an account yet).