New browser engine reports based on new browser engine detection of DeviceDetector

*First step of removing old UserSettings stuff (refs #3962)*

- updates DeviceDetector to latest version (and adds missing browser/os icons)
- old BrowserType reports (UserSettings plugin) has been removed / replaced with new browser engine reports in DeviceDetection plugin
- those reports will be much more accurate as before the detection was only based on a browser name > browser engine mapping
- browser eninge is now stored in a new db field
- browser engine is also available for segmentation
Ok maybe you can change the DeviceDetector method to return gecko first? Or we can change the fixture to generate a Webkit visit.