Wrong spendable balance for accounts with too many open orders

[ebma]

If an account has more than 10 open orders, the calculated spendable balance is wrong because since not more than 10 open orders are fetched, the app assumes that there are only 10 and reduces the balance by 5.0.
If the user hits the "Load more" button below the list of open orders and fetches all orders this way, the spendable balance is correct.

In order to fix this, we might need to fetch all open orders because this affects the calculated minimum amount for trading and sending payments.