Changing flask-security to flask-security-too

[tuz666]

I opened this new branch because the previous got messed up during a rebase.

The currently used flask-security package is no longer supported (latest change is 2,5 years old), flask-security-too is the maintained up-to-date version of it.

Previously we talked about @gammaw that introducing the authentication made the frontend page is a bit slower.
This new security package offers some performance boost with version 3.1.0 and 3.2.0, for these uplifts we need a modification which looks like a DB change but it's not that. I checked the use of lazy parameter according to this article and it looks like we don't use it directly anywhere in the code, so no other changes needed.

We agreed that we should do some performance measurement before these upgrades:

• @gammaw suggested to do a profiling on the front end page to see exactly how much time each transaction takes
• I recommended to extend our CI with a robustness/benchmark test which can simulate a big load of incoming GET requests and measure the time it takes.

I extended the CI tests with the robustness/benchmark part, you can see the results for flask-security-too version 3.0.2 here and 3.2.0 here, it wasn't a big performance break-through :(

[gammaw]

Go, go! Big up for the robustness tests addition!