paypal: Start support for multiple currencies

For now, ignore everything that is not the primary, and do not use the
converted total.

This is based on http://i.imgur.com/TNcLbPB.jpg
as I have 0 in all currencies for now.
paypal: Proper multi-currency support

An account per currency.
And fix xpath (missing ".").
paypal: Fix balance parsing with a single currency account
paypal: Support "american" balance style

Sources: http://i.imgur.com/rtcuMDa.jpg http://i.imgur.com/TNcLbPB.jpg