Update to v1.7.1

* New features
  - [ExternalCameraHook] Add externalcamera.cfg config interface
    - The interface is built into project when VIU_EXTERNAL_CAMERA_SWITCH symbol is defined.
    - It is automatically activated with the external camera quad view.

![External Camera Config Interface](https://github.com/ViveSoftware/ViveInputUtility-Unity/blob/gh-pages/assets/img/external_camera_config_interface.png)

* Changes
  - Now you can fully disable the binding interface switch by removing the VIU_BINDING_INTERFACE_SWITCH symbol
    - That means nologer

* Bug fix
  - [ViveRole] Fix HandRole.ExternalCamera not mapping to tracker in some cases
  - [ViveRole] Fix ViveRole.IMap.UnbindAll() to work correctly
  - [BindingInterface] Fix some info updating and animation issue
  - [VivePose] Now GetPose returns Pose.identity instead of default(Pose) for invalid device

Author: lawwong