Before we used insecure python variables to assemble a query string.
Now we use the DB-APIs parameter subtitution.
pymysqlite was switched for sqlite due to being included in python.

Currently we only need the db to keep track of the files that were
already downloaded, thus we only use one database and only one table.
A complete sql database is a bit too bulky for this purpose.
By using sqlite we can minimize and embed the db.

- mysql creates database and tables to given mysql if not existent already
- mysql reads last change values from db
- mysql saves ch_date after downloading
- run now takes care for the variables of mysql and studip