Description

Add a new TestDataSet with 3 sites so that we can test the population module and also the biasfield correction module.

Tasks

• Add new branch with a multi-site dataset to TestDataSets
• Test that this runs

How to test

Just run it. It should only run the population module. Note that I only added 2 sites with 2 subjects to keep this light-weight.

Release notes

Required: summarize the changes for the release notes here