Numbas data management features

[ublefo]

Description

• Implement methods in task_definition model for numbas data management
• Implement routes in task_definition_api for numbas data managemnt
• Remove unused upload API in numbas_api

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Tested with https://github.com/thoth-tech/doubtfire-web/tree/add-numbas-integration

• File upload
• File download
• File deletion

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation if appropriate
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have created or extended unit tests to address my new additions
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules