Upgrade/element-web v1.11.17 : fix linter

[estellecomment]

Fixes the CI for "Static Analysis", "ESLint". Changes were made in element-web 1.11.17 which broke it.

• prettier is used as a formatter. It uses eslint's config in this case. It does not have a warning mode, so it errors on our files. I disabled it.
• eslint wants a standard version number. So we use 4.1.5-1.11.17 instead of 4.1.5_1.11.17. We have to watch out for deployment script breaks.
• our code does not follow all the new style rules that were added. So for our code, I replaced errors with warnings, until we have them all fixed. We can fix them as we go when we edit the files.
• we are also linting module_system which is not our files. So I removed it.

Note : things would be simpler if all tchap code was in a single directory, so that we would only lint our own files. Also nice for devs to understand which code is which.

[gitguardian]

️✅ There are no secrets present in this pull request anymore.

If these secrets were true positive and are still valid, we highly recommend you to revoke them.
Once a secret has been leaked into a git repository, you should consider it compromised, even if it was deleted immediately.
Find here more information about risks.

---

<sup><sub>🦉 GitGuardian detects secrets in your source code to help developers and security teams secure the modern development process. You are seeing this because you or someone else with access to this repository has authorized GitGuardian to scan your pull request.

Our GitHub checks need improvements? Share your feedbacks!</sub></sup>