support for vive trackers

[joreg]

helo,

i want to add support for vive-trackers. before i go full pullrequest, here my thoughts:

to my understanding those would be unique to OpenVR but still they would be added to the VRDevice class. right?

so in VRDevice.cs right next to:
public abstract TouchController LeftHand { get; }
i would add a
public abstract Tracker[] Trackers { get; }

i'd add an abstract Tracker class which would be similar to the TouchController class and would add an implementation for it for OpenVR and empty implementations for the other vr-sdks.

please let me know if this is going in the right direction or not or if there other things to consider?

[xen2]

Thanks for offering help.
Sure, sounds good to give it a try with this design.

[joreg]

here is my PR #213