add datatable function to export members list

[hugosolar]

Fixes creativecommons/tech-support#399

Description

Add export buttons to datatables to copy table data or export it as csv
This option works only for global network administrators

Other information

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the master branch of the repository.
• My commit messages follow best practices.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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