fiat: Expand currency offering

[carlaKC]

As is, we only obtain fiat quotes in USD. More options would be nice for non-dollar denominated users.

[Possible solutions, still in progress]
Investigate whether coincap (currently used price backends) provides other pairs. If not, look at other backends (also relevant for #37) or look at converting BTC -> USD -> Other Currency. Preferably the first option, since each conversion loses accuracy.

[carlaKC]

I think that the solution we have in #122 is a more flexible way of allowing multiple currency options. We can sink endless resources into adding new backends/ currencies, so let's rather allow use of the reporting functionality with custom data and re-open this issue if there's demand for additional built in currencies.