Launch test for Baker 4.0 (shelf)

The requirement to be part of the Baker 4.0 launch and help us releasing it is to have a magazine "ready" (or almost ready) to be released on Baker with a shelf and periodic releases. Given the current feature set, this means:

1. The magazine must be free, at least at the beginning (we don't support In-App Purchase yet)
2. The Hpub of the magazine ready
3. A server to host it

Why Baker needs you

The most important thing, the reason why we need your help, is because we have to be sure that Apple will approve the magazine with the current Baker 4.0 feature set. This means that:

1. Until Baker 4.0 is finalized, you start using it and testing it to tell us if it works. Please mind that there are probably still issues that need to be sorted out, see them here: https://github.com/Simbul/baker/issues?milestone=8&state=open
2. When we complete Baker 4.0, merging it back to master, you submit it to the App Store and tell us when it gets approved or if not, which are the reason for rejection.

Getting started with Baker 4.0

Part 1, until the shelf branch is ready

1. Download the current working version from: https://github.com/Simbul/baker/tree/shelf
2. Prepare the shelf JSON on the server
3. Upload the Hpub magazine on the server
4. Test it. :)

Part 2, when it's ready for release

1. Download the release candidate (will be in master at this point)
2. Prepare the shelf JSON on the server
3. Upload the Hpub magazine on the server
4. Test it. :)
5. Submit for approval on the Apple App Store (it's not necessary to make it immediately available, we just need a proof that it passed the Apple approval process).