Send invoice by email

Minimal version because we're missing time
depends on #35 
closes https://github.com/my-koop/service.website/issues/310

If approved, we will have to make react and moment dependencies in service.website instead of dev-dependencies.

Currently only generates a report in english. 
Could be solved with https://github.com/my-koop/service.website/issues/144

![image](https://cloud.githubusercontent.com/assets/4157103/5337390/d4c9928e-7e95-11e4-91f8-210ce16fdd2e.png)