Include PartnerID param in eway_rapid requests if set
added standard error codes to usa_epay
Merge pull request #1456 from Shopify/usa_epay_standard_errors

Usa epay standard errors
added standard errror codes to mercury
Merge pull request #1457 from Shopify/mercury_standard_error_codes

added standard errror codes to mercury
Merge pull request #1460 from Shopify/eway_rapid_partner_id

Include PartnerID param in eway_rapid requests if set
Updates CHANGELOG with Authorize.net/Stripe ApplePay support and eWAY Rapid PartnerID
GlobalTransport: Truncate order_id

From their docs:

http://cl.ly/image/2H0h1X2o2N3N/content.png

They allow 25 characters for InvNum for all cards except Amex for which
they allow only 16 characters.  I'm not sure why they'd distinguish
based on card brand.

We'll truncate to 16 characters for this gateway to be consistent across
the board.  Hopefully this will help customers find out sooner rather
than later that the max is 16 for some card types.