Add minimal two-track catboost line

This MR is a minimal version of !437 (closed) that adds a 2-track MVA line based on a catboost classifier. Model evaluation code lives in device/vertex_fit/two_track_catboost. This is handled by the algorithms two_track_preprocess and two_track_evaluator. Unlike !437 (closed), there is no attempt in this MR to develop general machinery for evaluating catboost models. The selection is handled by the two_track_catboost_line. These algorithms are added to the default HLT1 sequence. The catboost line appears to perform better than the default 2-track MVA line. In MB events, we get:

Hlt1TwoTrackMVA:          82/  4999, (  492.10 +/-    53.90) kHz
Hlt1TwoTrackCatBoost:     79/  4999, (  474.09 +/-    52.92) kHz

In Bs2PhiPhi, we get:

Hlt1TwoTrackMVA:        1795/  5000, (10770.00 +/-   203.52) kHz
Hlt1TwoTrackCatBoost:   1853/  5000, (11118.00 +/-   204.90) kHz

This indicates than we get about 5% better efficiency at a 5% lower rate.

FYI @apearce