Perform validation for upload

When a user uploads data, they pass in a data block and also specify absolute bounds. It is possible for these to be in conflict (ie a user has a z-range of 2 for a single image slice).

There should either be a validation step before upload to guarantee that the ranges agree. Alternatively `(xmax, ymax, zmax)` should be optional and mano should infer the dimensions from the data block size.