Rename Assign() to CopyIn(). Implement CopyOut().
Add method PlexSize(), returning number of matrices in the plex.
Add make variables to get mkFit compile with root and produce validation plots (host only).
Add method OutputFittedTracks(). Make method names clearer. Follow up on renaming of Assign() to CopyIn().
Follow up on renaming of Assign() to CopyIn().
Add default constructor. Make state() return a ref, as all other access functions.
Implement separate function make_validation_tree() to do sim/rec track comparison. Both fitting functions now return fitted tracks in a vector (so far this is only done if compiled with ROOT for validation).
Follow up on changes in fittest: prepare output vectors, call validation function when compiled with ROOT.