Add scaffolding for BidirectionalPathTrac{ingRenderer,er}

Also add hollow sphere scenes that uses BidirectionalPathTracingRenderer.
Add Sensor methods to sample/compute spatial and directional We seperately

Also implement for all sensors.
Add scaffolding for PathVertex class
Generate light samples for BidirectionalPathTracingRenderer
more scaffolding WIP
implement more samplenext WIP
WIP for light vertex
Use SI vertex
add contribution
handle more
calculate weights
Add debug info level 1
add level 2 debug
add unweighted
add w