Improve extensibility for custom server-side payment processors
Implementing a custom server-side payment processor is a process that suffers from a few minor, but quite annoying issues. In this pull request we address the following issues:
1. Remove unsafe yaml loading warning coming from production settings
2. Fix empty checkout button for custom server-side payment processors
3. Add custom urls for custom payment processors. This is useful, e.g: for callbacks.
4. Fix http/https url scheme for those people who don't run ecommerce with https in production. This might happen, when running locally, for instance.
Is not a better time to review this? If not, do you know when this could be taken in?