RV-333: Fetch Prices Using New Functionality

### Summary of Changes:

Now that we're not using ```hiku_data``` anymore. We will use ```getListingData```.

The process runs as follows:

#### FundClass without Instrument ID:
- we fetch valor number first
- Using valor number we list all existing exchange codes with the fundclass currency.
- we generate instrument identifier for each exchange code.
- we fetch prices for all instrument ids. 
- we detect which instrument id that has the most up to date price and return it a long with the price and date.

#### FundClass with Instrument ID:
- That is an easier solution. if we've an instrument id then we can fetch prices directly.
- To make process faster, we can fetch prices for multiple instrument ids at once. SIX accepts up to 200 ids. I splitted IDs to chunks where each chunk contains 100 IDs.

Generally when exception happens we store the error message along with necessary data. Then we can retrieve all exceptions using ```client.exceptions```. 
Why? Isn't ```nil``` default anyway?