Multi currency

This branch adds support of multi-currency. Best way to test this is to add an item with starting bid defined in different currency than default (euro). The price should appear everywhere in euros after adding the item. Minimum starting bid is always 1 euro, so for example minimum starting bid in SEK would be 11,14 (at the moment of writing this).

Since currency conversions rarely rounds to whole numbers, I changed prices and bids in application from int to float, as a quick fix. Bidding on items (that were added in different currency) may be a bit funky as inputs fields have step-attribute set as "0.01". Best fix in my opinion would be to save all prices and bids as integer values representing cents (1 euro -> 100 cents) and display the number in euros (and convert that value to different currencies).

As a small addition to everything else, this branch also changes the way auctions are displayed on profile page, as previous way didn't handle large amount of auctions well.