Added EVO Canada gateway

Here's an integration for <a href="http://www.evocanada.com/">EVO Canada</a>.  There are some explanatory notes in the module docs about how transaction ID vs. auth code is handled.  The remote tests all run with their test account.

One note is that EVO has both refund and credit actions.  I put both in, but wanted to point that out as AM used to use credit and now favours refund.

Hopefully this works for you all – let me know if you need anything changed.