Reorder currency pairs for trade

I haven't tested it yet, but basically this pull request consists on adapting what @vhpoet did in 

77a11af31bf44875f19935ed9ea6fa8e2c412602
and
1a44e94844d6948d103e31c6121dcb71d5b65ef1

to close #265. This time is to order the currency pairs at the trade page.
Please, take a look.