Added CombineScanGroup

CombineScxanGroup makes a 3D data set from a WorkspaceGroup of scanned images
refs #301
Added WaitCancel Algorithm

Added a silly little algorithm, WaitCancel, which runs until it is cancelled.
I changed the SINQCCDListener code to check if this is running. If not,
abort. This is now mostly working, only starting WaitCancel from SINQCCDListener
still dumps core reliably.

Refs #301