change lidar odometry model to use scan pose pointers

[nickcharron]

Right now, the lidar odometry stores all active scans in a list, and then passes them as they come in to the scan matcher class. For the case of the scan to map, this won't have any duplicate data because the registration class doesn't need to store to scan pose. For the case of the scan to scan registration class, it actually copies the scan poses and saves them in a list of reference scans which means this data is duplicated (and it can be a lot of data, depending on our lag duration and number of neighbours).

If we store shared pointers to the scan poses and pass those to the scan registration (and it stores the pointers and not the data) then it will eliminate data duplication.

CAUTION: the lidar odometry will be updating the pose of the ScanPoses which will affect the scan registration. We need to make sure this doesn't cause any adverse effects.