Allow turning off normalization in CLI

[lacan]

Linked to a previous issue, wherere the cellpose team allowed for normalization to be turned off via a notebook, I would like to request that normalization be turned off via the command line call to cellpose with e.g. --no_norm so that we may implement our own normalization procedure.
This is especially important when working with giant slabs of data where the prediction is done tile by tile.

[carsen-stringer]

good point @lacan , this is added now to the github version, will make a new pip soon