Refactor: Annotate Hashes with Suffixes throughout the System

This adds hash suffix annotations to all the content hash creations I found throughout the system. The idea is to do this migration gradually... For now, hashes are only annotated, but the `shash::Digest<>` interface is backward compatible and shouldn't break anything in the legacy code base.

I need those hash annotations in the garbage collection, otherwise I would be forced to hand the information about *what* is actually deleted too deep into the system.

**Note:** This Pull Request depends on [Feature: Hash Wrapper Extension (Suffixes and MakePath)](https://github.com/cvmfs/cvmfs/pull/499)