Add currency_rate setting; Rename field payee_name to payee

[iofjuupasli]

It allows to multiply values from source csv to transaction rate. For case when bank account in one currency and ynab account in another.

Also payee_name renamed to payee. This way ynab native csv import works correctly

[nielsmaerten]

Sorry, but setting a currency rate is out of scope for this project right now. I think this use-case is pretty rare.
(I could be wrong of course. In which case: start voting)

Here's my reasoning:

1. currency rates are not constants. exchange rates change every second
2. different transactions will have different exchange rates, making it impractical to set them in the config file
3. you'd have to pull the exchange rate from an external API, looking up the historical rate at the time of the transaction
4. even if you were able to get the exact rate, the exchange rate charged by your payment provider may be different
5. all this can cause transactions in YNAB to have different amounts than what appears on your banking statement
6. and finally... that will cause issues when reconciling

[iofjuupasli]

I agree with all that.

In my case it's still very useful, and differences in rate I compensate by eventually making "Manual Balance Adjustment". Since I use it for personal budget, the perfect reconciling doesn't really matter. So I'll use my fork