add net to wizard recommendations

This is the data model change that I mentioned for fixing suggested in bolus tooltips @brandonarbiter 

As discussed with @kentquirk and @jh-bate also.

I'm not particularly attached to the word `net`, but I do prefer it over `total`, which I think could be misleading, given that the value will often be less than the sum of the `recommended.carb` and `recommended.correction`.