Add a default value for the setup option.

[dylanahsmith]

@kevinhughes27 & @EiNSTeiN- for review

Depends on and include pull #24, see the last commit for this pull request's changes

Problem

Right now we have boilerplate code generated for the omniauth setup option in shopify_app, which basically prevents us from making any improvements to it without updating all those apps. For instance, we have a fix_https method which seems to only exist for the purpose of working around old setup lambdas that don't prefix the url with http:// instead of https:// (e.g. commit aa533f0 fixed the setup lambda in the README).

Also, we should have a default just to make the gem simpler to use.

Solution

Use option :setup,... to set a default proc to use for the setup.

Possible Enhancements

We might want to consider allowing merchants to enter their shop name without the .myshopify.com suffix and having the setup handle that automatically for the authorization endpoint that just redirects to Shopify. For now I have just added a test to show how that can be done.

[kevinhughes27]

lgtm - I never even stopped to consider that this code was duped everywhere - nice fix!

[EiNSTeiN-]

👍