Changes

Structure '''trailer_def ''' was greatly improvedand redesigned. Old system with list of trailers for given cargo is used for rest of old trailers only (using cargo folder placement with filled '''trailer''' and fake underscored trailer body types).New fields support system that matches cargoes to trailer only through trailer body types with additional information. Most important are trailer gross weight limit'''gross_trailer_weight_limit''', body type '''body_type''' and country validity'''country_validity'''. Then there are cached/precomputed trailer mass'''trailer_mass''', '''body_mass''', '''volume''', '''axles''', '''length ''' and chain type'''chain_type''' for fast access without loading all accessories as well as data for trailers that do not have all accessories well defined (eg freight market ones). In adition , there are also cog placement parameters- unlike older mechanics right now its plain cargo cog offset in meters (before was height in halfs due to historical reasons).