Implement rate limiting with Flask-Limiter

[Glandos]

We currently have a number of issue with rate limiting, in login, admin or invite forms.

@0livd implemented a custom made LoginThrottler in #249 that served well, but is limited. I open this discussion to the usage of https://flask-limiter.readthedocs.io/en/stable/index.html This has the main drawbacks of adding more dependencies to the project, but can effectively increase the security for every user.

@0livd do you have an opinion on this new dependency, since your code will be obsolete in the case we use Flask-Limiter? And for everyone, do you have experience with this? Otherwise, I am willing to perform some tests with this.

[almet]

Hey, thanks for opening this. Using Flask-Limiter seems a good way to move forward on this. It's easy enough and seems maintained. It's okay to have one more dependency for stuff like this in my opinion.

Cheers.