Managed to get traffic shown up in Maps. However, traffic doesn't automatically load when panning the map, either the codes don't have it or I haven't found the codes responsible for this yet.

The changes are: make traffic toggle visible in MapSettingsUI.qml, fix un-comment traffic setting loading/storing in MapApi.js, and fix the wrong function argument for trafficObject.requestTrafficAt() in MapApi.js (original code doesn't have 2nd argument for requestTrafficAt(), the argument is radius in km btw). By doing these, traffic show up, just doesn't auto-refresh when panning.