trezor: implement "backend" support for p2sh-segwit and native-segwit multisig
trezor: implement "backend" support for p2sh-segwit and native-segwit multisig

vialectrum/vialectrum,asfin/electrum,cryptapus/electrum,pooler/electrum-ltc,cryptapus/electrum,neocogent/electrum,pooler/electrum-ltc,kyuupichan/electrum,fujicoin/electrum-fjc,neocogent/electrum,vialectrum/vialectrum,spesmilo/electrum,wakiyamap/electrum-mona,wakiyamap/electrum-mona,kyuupichan/electrum,kyuupichan/electrum,vialectrum/vialectrum,fujicoin/electrum-fjc,wakiyamap/electrum-mona,pooler/electrum-ltc,neocogent/electrum,asfin/electrum,pooler/electrum-ltc,asfin/electrum,spesmilo/electrum,cryptapus/electrum,wakiyamap/electrum-mona,fujicoin/electrum-fjc,spesmilo/electrum,spesmilo/electrum