Add Support For Key Module

Please try out the dev version and let me know if it's working the way you intended.

In the form, I added an option to select Key Module and then expose two fields, one for the site key and one for the secret key. I also added a service to grab the available keys from the key module and populate the dropdowns. I added two helper functions in the module and used suggest for the key module rather than adding it as a dependency. The only issue was that the original form fields for site key and secret key were required so I had to enter some placeholder values to save the form. I tried to create a patch with my changes and have added it to the comment here.