Support arbitrary kwargs in dask.array.fft

[jakirkham]

Would be nice if the wrapper/wrapped functions in dask.array.fft supported arbitrary kwargs. That way implementation specific arguments could be passed on to the underlying FFT function.

Might be a little work if we wish to validate these arguments during graph construction. Alternatively we can just trust the user and raise at runtime if errors like this occur.

[jakirkham]

Might want to include norm ( #3280 ) this way as well.