Make it easy for Child Algorithms to post progress through their parent

[NickDraper]

Extend the CreateSubAlgorithm method to take another two Paramters.
- ProgessScaleFactor default 1
- ProgressOffset default 0
Then wire up the parent algorithm to listen to the progress events of the child scale and offset them appropriately and then send them from the parent.

Warning: consider that there may be more than one sub algorithm per parent.

RebinToWorkspace is a good example case for the need for this.

[NickDraper]

This issue was originally trac ticket 379