[WIP] Tabular dataset + Doc for testing the advantage of using DA techniques

[YanisLalou]

Issue #19

Dataset implemented: https://tableshift.org/datasets.html#childhood-lead

Still need to be done:

• For the plot_domain_adaptation_advantages.py:
  • Plots ?
  • Understand why score gap between with and without DA technique is so small
  • rename office31 fetch functions
  • Change doc depending on DA results