v1.0.3: [Shopify] Dynamic myshopify.com subdomain (#77)

* Dynamic myshopify.com subdomain

The oauth domain is not a constant with shopify - each store hais on its own subdomain.
The current setup of defining a subdomain in the services config array will not work when for example installing an app or sales channel from the Shopify app store. The subdomain value need to be dynamic from the shop GET parameter.

This PR swaps out the current subdomain config item for the shop param in the current request.
I don't think this is the ideal solution, but it works and at least gets the ball rolling to sort out the issue.

I have implemented it to have no breaking changes - if the subdomain is set - that will be used, if not it will fallback to the shop param on the request.

* code style fix

.. I think

* StyleCI doesn't tell you exactly what wrong

so guess work here