[WIP] Handling of binary content in actions and events

[dereulenspiegel]

I would like to implement an instagram bee in the future and would like to generally have the ability to handle media files for other uses. So as a first step I created a new type called * BinaryValuewhich can hold anio.ReadCloser` and a string describing its type. Since I am completely new to this project I would like to get some feedback whether something like is wanted/needed and if so if I am on the right track to create something which can be merged in the future.