Chunk size needs to be dynamic

[bahanonu]

Chunk size needs to be dynamic or some percentage of the input x-y size else get the below crash (e.g. if image_masks is [250 241 225]). I'll push a commit with this change.

Error using types.untyped.DataPipe/set.chunkSize (line 113)
`chunkSize` must be within `maxSize` bounds

Error in types.untyped.DataPipe (line 48)
            obj.chunkSize = p.Results.chunkSize;

Error in add_processed_ophys (line 72)
    DataPipe=types.untyped.DataPipe(maxSize,...

[bahanonu]

See #6.