Base: Implement TimeElapsed

Some instances of TimeInfo serve the sole purpose of measuring time
duration. Using system time is unfortunate as it returns wall clock,
which is not guaranteed to be monotonic. Replace such a usage with
the new TimeElapsed class based on steady clock.

src/Gui/DAGView/DAGModel.cpp

@@ -460,7 +460,7 @@ void Model::updateSlot()
   //for speed. Not doing yet, as I want a simple algorithm until
   //a more complete picture is formed.
 
-  Base::TimeInfo startTime;
+  Base::TimeElapsed startTime;
 
   //here we will cycle through the graph updating edges.
   //we have to do this first and in isolation because everything is dependent on an up to date graph.
@@ -761,7 +761,7 @@ void Model::updateSlot()
 
   //Modeling_Challenge_Casting_ta4 with 59 features: "Initialize DAG View time: 0.007"
   //keeping algo simple with extra loops only added 0.002 to above number.
-//   std::cout << "Initialize DAG View time: " << Base::TimeInfo::diffTimeF(startTime, Base::TimeInfo()) << std::endl;
+//   std::cout << "Initialize DAG View time: " << Base::TimeElapsed::diffTimeF(startTime, Base::TimeElapsed()) << std::endl;
 
 //   outputGraphviz<Graph>(*theGraph, "./graphviz.dot");
   graphDirty = false;