Add proper UFO process integration

Ok, this is the fruity Python side of this mornings hard labour. I will add an example to concert-examples but you can get a first impression from the module docstring.

Some outstanding issues: 
- Naming ok?
- What about futures? The problem here is, that the user _must_ notify `InjectProcess` that no more data is to be expected. So we might wrap the `run` method with `@async` but in any case the user must interact with the process by pushing and stopping.