start setting up structures for a THICK Tracker. Reuse some of the PARALLEL-T trackers routines to get things started. Need to move common routines to Track if we will use them for more than the prototype. The THICK tracker is a MSc thesis and will reside in a own branch as soon as the structure is ready

fix opt-pilot tests failing after using OPAL's SDDS parser by updating to an SDDS stat file from recent OPAL version

Fixing mean momentum as discussed in #183; adding OFFSETP to add momentum shift relative to reference particle