to RunnableDB to allow full benefit of dataflow graph capabilities.
- Removed from Extension.pm branch_code, analysis_job_id, reset_job extensions to
  RunnableDB (no longer trying to shoe-horn hive 'extra' functions into them)
- Bio::EnsEMBL::Hive::Process mirrors some of the RunnableDB interface
  (new, analysis, fetch_input, run, write_output)
  but uses a new job interface (input_job, dataflow_output_id) instead of
  input_id (but provides convenience method $self->input_id which redirects to
  $self->input_job->input_id to simplify porting)
- Changed Worker to only use hive 'extended' function if the processing module
  isa(Bio::EnsEMBL::Hive::Process).  Also allows all RunnableDB modules to
  still be used (or any object which implements a minimal 'RunnableDB interface')
  (new, input_id, db, fetch_input, run, write_output)