Clusters should be savable

[numeredev]

DESCRIPTION

Is your change request related to a problem? Please describe.
It is not optimal that only tables are allowed to be used together with save and export.

Describe the solution you'd like
I also want to save or export the contents of a cluster using those commands.

Describe possible alternatives you've considered
An alternative could be to write a plugin overriding those two commands patching the necessary functionality in.

Additional context
Add any other context or screenshots about the feature request here.

(Do not write below this line)

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DEVS' SECTION

ANALYSIS

(Describe, what's the issue and which changes have to be made)

IMPLEMENTATION STEPS

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• Implement the necessary changes in a new branch created here on GitHub
• Test your implementation

DOCUMENTATION STEPS

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• Update the changes log
• Add comments to your implementation
• Add Doxygen documentation comments
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• Update the language strings (*.NLNG files, if needed)

PULL REQUEST

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