Technical upgrades

[ntarocco]

The app should go through various technical upgrades.

1. we need to upgrade react-searchkit to the latest, and therefore, axios. This is not easy, because the NodeJS version might have to be upgraded, leading to a certain number of tests failures. For now, we had to pin cheerio to a specific version, and this should be removed at some point.
2. we should upgrade NodeJS. However, this mean upgrading npm, and the biggest change is that, by default, newer versions of npm than the current v6 install peerDeps too. This cause issues. A workaround is to add the param --legacy-peer-deps to all npm command to simulate the previous behaviour.
3. enzyme is completely abandoned. Anyway, in my opinion, snapshots testing did not turn out to be particularly useful. I propose to remove it entirely and tests too. For new test, we could use React Testing Library.
   If it is to be kept, or you the error that TextEncoder is not found, this commit should be added here too.
4. we could explore removing craco, and come back to the default create react app. It was added because create react app does not support LESS by default, and it is suggested by the React SemanticUI doc. Today, there could be better ways. If this is done, then we need to remove the aliases defined for webpack.
5. we should probably use the invenio linter rules.
6. what about upgrading React?
7. partial upgrades done in Upgrade npm #629