Payment order ( request #3684 )

On this branch I will develop add the bitcoin implementation related to the feature request #3684

In order to make my future implementation of bitcoin, and to provide a way to make sure that a payment is not already processed I created a new schema. We can choose to delete it after a transaction is made or keep it for record, but it can protect from a malicious user updating his result page and therefore obtaining more gem(after payment) .

For now I used bitpay and the subscription is not available yet, I want to find the right way to handle it in the views.