Handle cycles while rendering dependency tree to json

[nimatrueway]

This PR handles cycles in TreeView.createJson (used in task dependencyBrowseTree) the same way it is handled in Graph.toAscii (used in task dependencyTree).

The effect is:

• Top picture is dependency tree rendered into a json shown on a web page after this fix (task: dependencyBrowseTree)
• Bottom picture is the dependency tree rendered to ascii on console (task: dependencyTree)

[lightbend-cla-validator]

At least one pull request committer is not linked to a user. See https://help.github.com/en/articles/why-are-my-commits-linked-to-the-wrong-user#commits-are-not-linked-to-any-user

[lightbend-cla-validator]

At least one pull request committer is not linked to a user. See https://help.github.com/en/articles/why-are-my-commits-linked-to-the-wrong-user#commits-are-not-linked-to-any-user

[nimatrueway]

I did sign the CLA.

[eed3si9n]

At least one pull request committer is not linked to a user.

@nimatrueway Thanks for the contribution. I think the robot is complaining that the email used to make the commit is not associated with your GitHub account. If you used work or personal email make sure those are added to your GitHub account (you can hide them as private), or commit again under the correct --author.

git commit --amend --author="Foo <foo@example.com>" --no-edit

[nimatrueway]

Oops, so sorry! Thanks @eed3si9n for the nice tip. 🙏🏻

[nimatrueway]

Added copyright header to "TreeViewTest" to make checks pass.