Remove collector and save using common save().
Merge branch 'c-style-save'

- Remove collector.
- Remove feedback-channel.
- Use common save() method.

Purpose of changes:
- Optimize performance.
- Make I/O the same for Fastflow as the others.

Conflicts:
	code/particles/fastflow.cpp
	code/particles/fastflow_farming.cpp
	code/particles/fastflow_farming.h