Create bech32 addresses by default

[cmihai]

On the "Receive" page in the wallet, by default, created addresses are P2SH. Funds sent to P2SH addresses cannot be staked, and users will generally want to stake them. There was discussion to make bech32 the default address format in Unit-e; until that happens, the wallet can pass the required address type when the address is created.

[Ruteri]

I think the default should be legacy since commits can only use those.

@scravy @Gnappuraz