Move OutputStream to output Sequence to help AthenaMT scheduling.

This MR moves OutputStreams (that have the asAlg flag set, most of them) into the Athena Output Sequence to help with MT scheduling (@leggett , @tsulaia ). It also adds a mutex for writing that is currently needed if more than one stream is used (because writing modifies the SG proxy of the objects in the ItemList, conversion service caches file name for object placement, to be fixed later). Some tests for Registration Stream may need updating or they could be obsolete anyway (@cranshaw ).