Change iris dimensions to match the production system

[teor2345]

Currently we're using iris dimensions of 160x80, but the production dimensions are:

• [x] full resolution: 200 columns by 16x2x2 rows
• [x] medium resolution: 100 columns by 8x2x2 rows

As part of this change we could also improve performance:

• [x] make sure the polynomial sizes are tight

And ease of use:

• [x] make the polynomial size changes automatic by calculating them from the iris size

This change also needed fixes to the following design issues:

• [x] Split iris bit configurations and encoding configurations
• [x] Avoid confusion between the number of rows in a full iris code, and the number of rows per encoded block

And bugs:

• [x] Calculate polynomial sizes from the encoded size plus padding
• [x] Add missing impl EncodedConf for MiddleRes

[teor2345]

I decided not to change the assertions, because we might want larger polynomials for security or testing reasons.