Migrating from master and slave vocabulary

[bopopescu]

For diversity reasons, it would be nice to try to avoid 'master' and 'slave' terminology in this repository which can be associated to slavery. The master-slave terminology could be problematic for people in several countries which has the history of slavery like Romania, USA and many others. Thank you for considering the proposal. Let me know if any changes in the PR are needed, I would be happy to implement them.

[Lukas-Dresel]

Hey, sorry for the super long delay here lol.

I'm okay with all of the changes as they only change debug/output messages, except for the last one (in the SQL query updating the user) as I frankly don't know enough about that for sure to know that this won't break things.