JIRA INFRA-525 #action In Progress

The official flask-bootstrap is still not compatible with bootstrap 4.
The application basically only uses the main template and one macro.
It's easier to include directly bootstrap in CSEntry.
It makes upgrading to the latest bootstrap much easier and removes a
dependency.

Update to bootstrap 4.1.3

Added:
- jquery-3.3.1.min.js
- bootstrap.bundle.min.js (include popper but not jquery)

Note that jquery.slim can't be used.
We need for example $.getJSON for datatables.

https://black.readthedocs.io/en/stable/

The "REDIS_URL" variable is hard-coded in RQ Dashboard.

REDIS_URL was used by redis_store that is passed to Flask Session.
The url variable used by Flask-Redis can be changed by setting the
config_prefix.

1. Rename REDIS_URL to SESSION_REDIS_URL
2. Rename redis_store to session_redis_store
3. Use "SESSION_REDIS" config_prefix to initialize session_redis_store

This makes it clear that this Redis instance is used by Flask-Session.
REDIS_URL will be used for RQ.

This reverts commit 4ddde36f.

This broke the loading of fonts. Fonts directory should be excluded.

The browser caches the static files (js, css...).
Flask-CacheBust adds a hash to the URL of each static file to force
clients to redownload the files when changed.

In Flask, session data are stored in a cookie by default.
Using a server side session, there is no risk of putting too much data
in the session and transmissting a big cookie on every request
(only an id is sent in the cookie).

Redis is used as backend (without persistent storage).

- catch IntegrityError on patch
- disable autoflush (IntegrityError was raised before commit due to
autoflush)