Integrate other paper lists

[vlomonaco]

Add link to external paper lists:

1. https://github.com/optimass/continual_learning_papers
2. https://github.com/xialeiliu/Awesome-Incremental-Learning

[vlomonaco]

Also here: https://github.com/giangnguyen2412/paper-review-continual-learning

[vlomonaco]

Also... let's check if there are useful resources we need to add to the wiki looking here: Continual Learning: Towards "Broad" AI