Shopify/active_merchant — pull request #1460 by j-mutter (2014-11-13 17:40:27+00:00)
Title: Include PartnerID param in eway_rapid requests if set

Adds the ability to specify an optional `PartnerID` to be sent with requests to eWAY Rapid as per [their docs](http://api-portal.anypoint.mulesoft.com/eway/api/eway-rapid-31-api/docs/reference/direct-connection)

Currently we use `application_id` as the `DeviceID`, which is defined as:
> DeviceID | O | 50 | string | The identification name/number for the device or application used to process the transaction

So I think it makes sense to leave this as-is.

Remote tests passed with the new field locally, but the current ActiveMerchant credentials don't work.

Plz 2 review @girasquid @ntalbott @edward
cc @mhashemi86