Integrate the TBB based file processing into the Spooler

This contains the changes required in order to integrate the new TBB based file processing pipeline into the old Spooler code. The public API of the processing pipeline did not change significantly. The public API of the Spooler itself changed *not at all*.

Main changes:
* replaced calls to old to new processing pipeline
* removed old processing pipeline
* introduced a streamed upload into the AbstractUploader (replacing the old path based interface)
* removed the (experimental) Riak implementation for the moment

**Note:** this contains [New File Processing Pipeline based on TBB](https://github.com/cvmfs/cvmfs/pull/219)
**Note:** this contains [Add a Buffer template to util.h](https://github.com/cvmfs/cvmfs/pull/218)