Improve XLSX support

[numere-bot]

DESCRIPTION

Describe, what you observe or want to be changed:
It's only possible to read XLSX files, would prefer, if it is possible to also write XLSX files.

Describe, what you expect to happen:
Enable XLSX as output file type for exporting tables.

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DEVS' SECTION

ANALYSIS

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

IMPLEMENTATION STEPS

(see also our Wiki for implementation guidelines)

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

DOCUMENTATION STEPS

(see also our Wiki for further information)

• Update the changes log
• Add comments to your implementation
• Add Doxygen documentation comments- Create or update the documentation articles (*.NHLP and *.NDB files, if needed)
• Update the language strings (*.NLNG files, if needed)

PULL REQUEST

• Create a pull request for your changes
• Fill out the template
• Assign @numere-org/maintainers as reviewers

[numeredev]

Let's test this: https://github.com/troldal/OpenXLSX