UKB Test dataset

[olivierlabayle]

In order to improve testing it would be ideal to get some form of small sized fake UKB dataset. Benefits:

• Uniform data for tests from end to end, currently BGEN and BED files are different
• Reuse to test the pipeline project : https://github.com/olivierlabayle/UKBBEpistasisPipeline.jl
• Potentially improved run time performance on the true UKB dataset since the sysimage will be computed from this runtest

[olivierlabayle]

partly done closing