Allow to use the [Vive] object without the HMD connected

[hectorC]

I'm trying to use the Vive's controllers without the HMD connected. I already got one controller to work using a re-flashed Steam Dongle (tested with a Python script) but the [htcvive] Max object won't start or poll for controller data unless the HMD is plugged. I believe this would also allow the use of Vive Trackers without HMD. The controllers could aslo be used without the HMD by just plugging the Vive's breakout box and not the HMD and starting SteamVR (for either dongle or breakout box, the requireHmd var needs to be set to false in the SteamVR configuration file for this to work).