Improve the options for the block height to rescan from

Currently, we usually start from the Segwit block as a default. That could be improved upon:

Most users don't remember / haven't written down the birthdate of their wallet (the blockheight of their first UTXO). However, they might at least remember the calender year in which they started stacking. So, a nice feature would be to let them select a calendar year and then use the blockheight from 1. January of this calendar year.