Optimize the filling of share properties (done when cloning RooRealVar) by using a std::map

Signed-off-by: Wouter Verkerke <verkerke@nikhef.nl>
Use hash tables for server list sizes >= 1000 in RooAbsArg::addServer

Signed-off-by: Wouter Verkerke <verkerke@nikhef.nl>
Speed up RooWorkspace::import by using a has table for the internal Workspace collection if size is > 1000 and by speeding up the removal of the set which is cloned in the import. We don’t delete the set which calls safeDeleteList. It is not needed, the set contains a list of all the nodes, so we simply delete just one by one.

Signed-off-by: Wouter Verkerke <verkerke@nikhef.nl>