function Skeleton()
{
	this.bones = []; //array of bones
	this.global_bone_matrices = []; //internal array of mat4
	this.bones_by_name = new Map(); //map of nodenames and index in the bones array
}
returns an array containing N samples for this property over time using the interpolation of the track
@method getSampledData
@param {Number} start_time when to start sampling
@param {Number} end_time when to finish sampling
@param {Number} num_samples the number of samples
@return {Array} an array containing all the samples