added support for laser.pkl if they exist

[sinjax]

Gives the association from each point to the lidar channel for sensor 0 as discussed in #60

requires users to download: https://drive.google.com/drive/folders/1PL6N2QSNFjXQTFqpcM1IShOhnJCgSz73

@xpchuan-95 not sure if you want to include this but I thought I'd offer the PR :)

[sinjax]

for x in `ls <LASER_ROOT>/laser`; do x=`echo $x | cut -d . -f 1`; cp <LASER_ROOT>/laser/$x.pkl <PANDASET_ROOT>/$x/lidar/laser.pkl; done

is the expected location of the laser files