New spectral cubes PR

Fixed other commits appearing in the other PR. @Cadair, could you please close the other one?
It seems the when I plot a map returned from this does not have the coordinates right... however the `gmap.meta` seems right...  
I see however, that the `map.meta` from this is just a `dict` whether for any other map is a `sunpy.map.header.MapMeta`