First steps towards ACTS track convertor, together with simple unit test.

First attempt to start adding track conversion

Reformat, and make trkTrackCollectionToActsTrackContainer pure virtual

First attempt of converting measurements

Cleanup CMakeLists.txt for Attila

Temporarily add CLASSDEF for ConstVectorTrackContainer until better location found

Temporarily add ConstRefHolder and permanently add ConstVectorTrackContainer WriteHandle
Add specialisations for MultiTrajectory and TrackProxy