Replace gmx_large_int_t with gmx_int64_t

Most changes are only the rename:
gmx_large_int_t -> gmx_int64_t
gmx_large_int_fmt -> GMX_PRId64 (or GMX_SCNd64)
gmx_large_int_pfmt -> "%"GMX_PRId64 (with space for cpp)
SIZEOF_GMX_LARGE_INT -> 8
GMX_LARGE_INT_MAX -> GMX_INT64_MAX
GMX_MPI_LARGE_INT -> MPI_INT64_T
str_to_large_int_t -> str_to_int64_t
get_egmx_large_int -> get_eint64

Exceptions:
simple.h: Adding of new type
xdrd.c: Remove code for SIZEOF_GMX_LARGE_INT!=8
thread_mpi: Add MPI_INT64_T type
scanner.*: Insert #include for simple.h to fix macro issues

Change-Id: I99abbec0ecafb2580ddba89677a110c137e9abd6