Use caching features in SQL Alchemy

[fsteggink]

Follow up on issue #395, which is now closed.

Here Just mentioned the following:

From what I learned: the latest versions of SQLAlchemy (v2 I think and up) having caching-features internally. Our SQLAlchemy==1.3.8 and Flask-SQLAlchemy==2.4.0 are really old but upgrades failed earlier, at least will take time. In general I would prefer a solution via SQLAlchemy.

It is a good idea to check if this works well, so my fix in #394 can be reimplemented.