Added IL2M strategy

[iretes]

Implementation of the class-incremental method "Incremental Learning with Dual Memory" (IL2M).

[coveralls]

Pull Request Test Coverage Report for Build 13441318849

Details

• 90 of 101 (89.11%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 51.118%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
avalanche/training/supervised/strategy_wrappers.py	7	8	87.5%
tests/training/test_strategies.py	1	5	20.0%
avalanche/training/plugins/il2m.py	81	87	93.1%

Totals
Change from base Build 11572207189:	0.1%
Covered Lines:	14726
Relevant Lines:	28808

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💛 - Coveralls

[AntonioCarta]

Hi @iretes, thanks again for your contribution. Everything looks fine. You just need to run black to change the code style.
Can you run the command black . and update the PR?

https://black.readthedocs.io/en/stable/index.html

[iretes]

Thanks for your feedback, @AntonioCarta. I had already run black ., and I believe the issue was actually due to missing imports for quoted types. I've just fixed it.

[AntonioCarta]

Thanks again.