Evaluate async SQL usage via async SQLAlchemy extension and suitable drivers

[CrsiX]

It may be a performance improvement to use async SQL drivers together with SQLAlchemy. This has to be evaluated and tested carefully, though. As of now, the following async drivers seem to be available and maintained for SQLAlchemy:

• aiosqlite (SQLite) looks good for SQLite
• asyncmy (MySQL) seems to be pretty new but also pretty fast
• asyncpg (Postgres), since it's also nice to add Postgres support when restructuring something so deep down in the code base

Before that changes are attempted, some benchmarks should be made to verify if there's significant speedup available.