Add 'currency_sign_before_symbol' configuration setting

Allows you to determine if you want himBH10.00 or -0.00. Default is the latter.
[backend] Fix issues where elements sometimes would not be found with Capybara

This was *only* failing when running locally. Slightly annoying.

Turns out Capybara does not support nth-child(<num>), so we have to work around that. Work around is easy enough. Turns out then that the selenium webdriver driver does not support that work around. Hmpfh. So now we have both syntaxes used interchangeably depending on the example metadata stuff.

Conflicts:
	core/lib/spree/testing_support/capybara_ext.rb
[backend] Fix failing test in payments controller spec by using the right number
[frontend] use correct class to check cart total in coupon code spec
Simplify Shipment#to_param code

(lol)
Penderize annoying frontend test
[backend] Convert payment method ID to string in payments_controller_spec to fix text
Fix negative symbol in promotion adjustments spec