Added additional node-searching helper functions.

[Malcolmnixon]

The additional find_children() and find_child() methods are intended to assist in finding nodes. For example some movement providers need to find function or movement nodes under the controllers. This can be achieved by:

# Get left controller
var left_controller : ARVRController = ARVRHelpers.get_left_controller(self)

# Get left controllers pickup
var left_pickup : XRToolsFunctionPickup = ARVRHelpers.find_child(left_controller, "*", "XRToolsFunctionPickup")

# Get left controllers direct movement
var left_direct : XRToolsMovementDirect = ARVRHelpers.find_child(left_controller, "*", "XRToolsMovementDirect")

[BastiaanOlij]

Nice!