Upgrade IRMA-api-server

As communicated by IRMA, in their step to moving to a new IRMA api server implementation, they are releasing an update to the current one. We need to stay up to date. See the communication:

1. Update the IRMA api server and release to production/demo BEFORE 31 jan 2019
2. Report to Sietse that we have updated

```
Dear everyone,

I am mailing to everyone I know that runs or is otherwise interested in the irma_api_server, https://github.com/privacybydesign/irma_api_server. This email is about the future of the irma_api_server, its upcoming replacement in Go, and also about future emails like these.

Let me start with something to do:
*Please update your irma_api_server to the latest version as soon as possible, but at least before January 31.*
Otherwise, your irma_api_server will be incompatible with an upcoming version of the IRMA app, that we will release at that time. The reason is explained below.

1) The eventual deprecation and replacement of the irma_api_server
The irma_api_server has been very useful and important for the IRMA ecosystem, but it has its drawbacks; it is not very flexible, or easy to configure, or easy to experiment with. Ever since we switched to the Go programming language for the IRMA app, we have been planning to eventually completely switch to Go. Therefore, we have been working on a new IRMA server in Go, that will eventually replace and deprecate the irma_api_server. This new server has been designed to be:
- Easy to deploy and use in a multitude of environments and use cases,
- Simple to configure and easy to experiment with,
- More efficient and scalable across server farms,
- more easy to automatically test using CI/CD.
Additionally, the new irmaserver improves legacy issues, fixes shortcomings, and improves efficiency in the protocol that it uses when issuing or verifying attributes from IRMA apps. It will be released as a library for use in backend server applications, as well as a standalone server like the irma_api_server. This new server (simply called "irmaserver") will be mostly compatible with the current irma_api_server. Not entirely, but when the new irmaserver is released we will simultaneously release an update of irma_js that will abstract away the differences for you as much as possible.

2) End of life of the irma_api_server
In the migration to the new irmaserver there needs to be a compatibility mechanism that ensures that all IRMA apps works with both the new irmaserver and the old irma_api_server.  In order not to pollute the new server with legacy code, we have decided to implement this compatibility mechanism in the irma_api_server, with an update adding compatibility with the upcoming version of the IRMA app, which will be released on February 1. After that, irma_api_servers that have not yet been updated will become incompatible with the latest version of  the IRMA app. This is why it is necessary that all irma_api_servers are updated. *Once your server is updated, please let me know.*
After the update introducing compatibility with both the old and the new upcoming versions of the IRMA app, the irma_api_server will no longer be actively developed, apart from bug fixes and security updates. The new irmaserver will be released soon after that.

3) Future mails like these
IRMA is, by design, a decentral system: anyone can run IRMA servers without involvement of us (the Foundation). This is an important and distinguishing feature contributing to IRMA's trustworthiness, but it also means we (the Foundation) have no way to automatically update all IRMA infrastructure. Although we of course try to prevent making breaking changes, sometimes this is unavoidable. We have to prevent that this leads to a fractured IRMA ecosystem with incompatible apps and servers, which would lead to bad user experience and hurt adoption.
As an alternative update channel, we will henceforth sometimes send emails like this one. The release of the upcoming irmaserver will be announced like this too. If you do *not* want to receive these emails please let me know, but in order to keep the IRMA experience for users as stable and reliable as possible, *we strongly recommend anyone running an irma_api_server, or the new irmaserver after it has been released, to stay on this list*. If you know anyone who you think should receive these emails as well, please let me know.

Kind regards,
Sietse Ringers.
```

Story points: 1.0