Adaptation to the new openledger api

Openledger backend team has implemented a new api, which includes these methods:
1. /exchanges (returns the list of supported exchange options, i.e what asset can we exchange to what. It contains information about gateway fee for each exchange option in the list.)
2. /exchanges/{exchange_id}/transfer/source/prototype?destination_address=&destination_memo= (returns to a user a "prototype" of a transfer that the user has to make in order to exchange his assets (that he sent) to another assets using given exchange option.)
3. /exchanges/{exchange_id}/transfer/destination (Method allows to check the validity of the transaction in the blockchain. This method must be called by browser/client when user wants to exchange one asset to another, and serves to check whether wanted operation in destination blockchain can be performed or not)

Need adaptation to this new api. But /exchanges returns incomplete list of exchanges, therefore some coins must work with old api.

Start by tracing the exchange flow that calls the existing API, then compare it with the listed /exchanges and transfer endpoints. Done means the UI supports the new Openledger exchange flow while retaining the old API for coins absent from /exchanges; verify both paths with the project's existing tests or manual exchange flow.

Written by the indexing model from the issue text.