WIP: Adding a VELO tracking algo that splits clustering and tracking, no more hits created

This MR is really just meant as a way to simply share this code. It's not meant to end up in master like this.
The TestCluster class is currently still included here in one of the headers as it allows me to simply play with it independently of the LHCb stack.
In the end this will probably just be the VPLightCluster.
The VPTracking is currently being reworked by me and I will update it as soon as that's done, currently it's just a crude hack of an old tracking version.

The goal is to have the clustering split from the tracking again, as well as to implement @sstahl's idea to only use clusters instead of having clusters and hits which would be redundant. The current clustering works and the VPTracking produces the same amount of tracks, however, this has not been checked in a more detailed way.

fyi @rquaglia