add support for different trainer modes (in GUI)

i’d like the ability to set the mode of my trainer (KICKR) from within the Zwift app. TrainerRoad allows this functionality, where I can set the KICKR to SIM or ERG or RESISTANCE within the actual app, rather than having to run the Wahoo Fitness App on my cellphone and control it from there. This would serve at least 2 purposes; 1. eliminate one gadget from the mix, 2. allow the user to switch mid-ride to a different mode (sometimes I like to use ERG mode to warm up or cool down, or do an interval, without having uphill and downhill cadence changes.