Code review comment for ~jibel/ubiquity:advanced_features_dialog

I have nothing to add on the code changes themselves.

I have a done some tests with current 19.10 image + this branch on top of it. Apart from the selected translations still in english (but I see them in the template below and it makes sense to update the translations in a separate commits as discussed on IRC before the review), I didn't spot any major issues compared to the linked design.

Next/Back works as expected, even if going to the custom screen selection and back then (previous option still selected). However (and I checked that this isn't a regression from that MP), once pressing back from the custom screen, "Entire disk" is selected instead of "Something else". The previous advanced feature selection is still remembered though.

Just a note: there are some missing margins on the Cancel/OK buttons in the dialog compared to the spec.