message: app is now fetching BTC balance
diff: @@ -3,6 +3,7 @@ import { Coinbase, GetPriceResult } from "../../services/coinbase"
  import { CurrencyType } from "./CurrencyType"
  import { AccountType } from "../../screens/accounts-screen/AccountType"
  import firebase from "react-native-firebase"
  +import { Blockchain } from "../../services/blockchain"
  const getFiatBalance = firebase.functions().httpsCallable('getFiatBalances');
  @@ -108,7 +109,13 @@ export const CryptoFeaturesModel = BaseAccountModel
  // TODO
  })
  const update_balances = flow(function*() {
  - // TODO
  + const instance: Blockchain = new Blockchain()
  + instance.setup()
  +
  + const address = "xpub6CUGRUonZSQ4TWtTMmzXdrXDtypWKiKrhko4egpiMZbpiaQL2jkwSB1icqYh2cfDfVxdx4df189oLKnC5fSwqPfgyP3hooxujYzAu3fDVmz"
  +
  + const result = yield instance.getWallet(address)
  + self.balance = result.balance // TODO error management
  })
  return { update, update_balances }
  @@ -160,15 +167,12 @@ export const DataStoreModel = types
  rates: types.optional(RatesModel, {})
  })
  .actions(self => {
  - const update = flow(function*() {
  - // TODO
  - })
  - const update_balances = flow(function*() {
  + const update_balances = flow(function*() { // TODO move to an Accounts class
  // TODO parrallel call?
  self.accounts.forEach((account) => account.update_balances())
  })
  - return { update, update_balances }
  + return { update_balances }
  })
  .views(self => ({
  get total_usd_balance() { // in USD
  