add PermutedDimsArray method that returns PermutedDiskArray

[rafaqz]

Closes #240

[rafaqz]

Ok so to remove the recursive PermuteDimsArray I moved type parameters perm and iperm from PermutedDimsArray to PermutedDiskArray. But then I had to add a ConstructionBase dependency so we can use Flatten.jl/Accessors.jl etc on it (so Rasters and other things don't break). ConstructionBase.jl is tiny and will nearly always be loaded anyway.

Then there were some issues with parent access after changes to PermutedDiskArray, so I went ahead and swapped everything to use parent(a).

[meggart]

Looks good to me. Would you consider this change to be breaking?

[meggart]

I think adding the ConstructionBase dependecy is a good addition. I think there are several places in DiskArrays where we added unnecessary fields to types that might have lived in the type parameter only, so we could slowly replace these as well.