Simplify wallet registration UX flow

[bigspider]

After #252, we could consider rewording the screens in the wallet registration so that it says "Continue" instead of "Approve", except for the final step, which is actually the user approval that matters.

If possible, it would be even better to completely remove all the intermediate button presses: the user just keeps scrolling right until "Approve"/"Reject" is shown after inspecting the last key.

Once this is done, it's this flow of going right until the final step is feasible for the signing flow as well, although that's probably more complicated in that case.

[bigspider]

Mostly done in #270; only partially for devices not using NBGL - but it should come for free once all devices migrate to NBGL.