replace mavlink specific Pack with general ivory-serialize lib
smaccm-mavlink: update generator, cabal.in for ivory-serialize instead of pack
smaccm-mavlink: regenerate all messages to use ivory.serialize
flight: use ivory-serialize instead of mavlink pack. broken

NOTE: this change causes flight generator to not terminate!
it fails to create a file for ivory_serialize.c or generate
ivory_serialize_prim.h from the searchdir, so i probably goofed
something in there...