FSManager interface and first RawFSManager implementation

Defined the following:
 * FSManager abstract interface
 * RawFSManager implemented as a singleton with a single
   synchronized file stream
 * Single-threaded buffered I/O

Signed-off-by: Raffaele Aquilone <raquiloX>
RawFSManager unit testing added and some minor changes more

The following has been done:
 * RawFSManager unit testing
 * More debugging and several fixes in RawFSManager implementation
 * Makefile
 * General clean up of the IOUtil folders

Signed-off-by: Raffaele Aquilone <aquiloneraf@gmail.com>