First version of user feedback fixes

This patch contains a raw version for fixing feedback_fn.

The new mechanism works as follows:
  - instead of a per-Processor feedback_fn, there's one for each
    ExecOpCode, so that feedback for different opcodes go via possibly
    different functions
  - each _QueuedOpCode gets a message buffer, a method for adding
    feedback and a method for retrieving (parts of) the feedback
  - the _QueuedJob object gets a new attribute that is equal to the
    index of the currently executing opcode
  - job queries get an extra parameter called 'ticker' that will return
    the latest message on the current executing opcode
  - the cli.py job completion poll will show the new status if different
    from the old one

Of course, quick messages will be lost, as currently only the latest one
is available. Also changes between opcodes are not represented at all.

Reviewed-by: imsnah