storage: factor out 'JsonDB'
storage: factor out 'JsonDB'

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