[CHORE] Currency pairs in trade tab: update order

Update the order of the currency pairs in the Trade tab dropdown menu, requested by Phil. 
Reflects "the majors" and XRP vs "the majors," plus selected other currencies.
[CHORE] Update commenting in trade currencies

This updates the comments in the ordering of the trade tab currencies
[FIX] Trade tab pair ordering

Put in commas instead of periods
Merge pull request #1224 from ripple/fix/trade_pairs_ordering

Fix/trade pairs ordering