Improve transfer options and fee transparency#183

Transaction costs for investing and withdrawing money from the site could affect the return on an investments, but options are limited, and the total transaction cost is difficult to judge since different services may differ both in fees and in which type of exchange rate they use. It would be helpful if this was more transparent, for example if a total effective exchange rate could be estimated for the different options. And if you could do some analysis to see if there are options out there that would be worth adding in order to minimize transaction costs, or write a log post with some guidance on this matter.