The only translation so far is french, but more can be added. The browser language is used thanks to the HTTP languages headers. There are still some problems with the translation of some strings, I don't know why this is. See #12
Introduces the "rest" module, with reusable utils for flask applications (will be packaged as a flask extension later on).
This allows to isolate some behavior in the context of the web application so the API and the web application can behave in different ways.