Adding CLEAR-10 benchmark to Avalanche

[linzhiqiu]

CLEAR-10 website: https://clear-benchmark.github.io

Continual LEArning on Real-World Imagery (CLEAR) is the first continual image classification benchmark dataset with a natural temporal evolution of visual concepts in the real world that spans a decade (2004-2014).

I am the first author of this work -- in our work we also use Avalanche (such a great CL framework) to conduct our baseline experiments, and it is now time for us to contribute back to the community! I will assign myself to this feature request.

[AndreaCossu]

much appreciated, thanks @linzhiqiu ! Let us know if you need any help with the pull request 😄

[linzhiqiu]

I finished it! Just submit a PR.