GaudiAlg::ID optimisation

A small cleanup of the ID class used for histogram/tuple IDs in GaudiAlg.

Main change is to add a move constructor from a string (LiteralID) that better serves the common use class where temporaries are passed to the ID constructor. Tested with the LHCb stack reconstruction application, and overall almost halved the cost of the ID constructor in cases where std::string&& can be utilised.