Improvements to Acts / Trk convertors and tests

The main goal here to make the convertor more complete, but also to make the ActsEventCnv unit test pass (currently it fails, but returns success).

There were a few components to it:

• realise that the trackStates() method returns a reversed track
• make the dumper convert parameters back into proper global positions (which means teaching it about geometry context).. and fix some other minor bugs
• call fillSurfaces on the multi trajectory to rebuild the surfaces

None of this code runs in production

cc @tbold @pagessin @ncalace