Wiko Rainbow: How to get Lollipop Cyanogen CM 12.1 / fix NVRAM errors and recover your IMEIs

If you have a Wiko Rainbow and rooted / flashed / fixed it the wrong way, then it could happen, that you wake up with an NVRAM error in your WiFi-setting or in IMEI-related problems. I just wrote some short words about how to fix it...