Consolidate track types

At the moment many different track types are used throughout the HLT2 sequence:

• the PrTracks, which are specific to the track types before the Kalman Filter
• v1::Track, the "old" track type
• v2::Track
• SOATracks (aka v2::Tracks)

And different versions of containers (KeyedContainer and std::vector).

Ideally, we only use 2 types for tracks: The (maximally) optimized PrTracks before the Kalman Filter, SOATracks after the Kalman Filter.

At the moment v1::Track is still needed for the full Moore sequence (?).

To start with, can we get rid of v2::Track?

Opinions, comments?

(NB: This might also apply to other object types...)

• Write direct converters: PrTracks -> v1::Track: Rec!2470 (merged)
• Remove v2::Track from the "main" sequences and header files (where not needed anymore).