Sequencer need generate useful information during a command

A sequence is basically one command and it can last for quite a long time, some information about the status of the sequence need to be displayed.

For now, I've put too much intelligence in my GUI and I need to change that.
One solution is to make spsaitActor to generate keyword within a sequence :

• exposure number / total exposure number
• status of individual command

That's would be a good start.