First step of a somewhat testable user management. - I know, the JSON returns are in an ugly format but the JS expects it that way. So let's keep it that way until we have time to fix the JS in the future.
This patch wil warn the user of the consequences when resetting the password and requires checking a checkbox (as we had in the past) to reset a password.
Furthermore I updated the code to use our new classes and added some unit tests for it 👯
Fixes https://github.com/owncloud/core/issues/11438