Estimator lazy refresh

.. Refresh model estimates when rides added, deleted, saved.

.. Lazy refresh will cancel any pending or running threads and
   trigger a new one in 15 secs time.

.. This strategy allows us to call a lazy refresh even when importing
   large number of rides, since the start will be delayed and cancelled
   by the next ride added etc.

.. The thread stop() function is also called by the destructor to stop
   when the user exits and avoiding delay/SEGV on exit.

src/Core/RideCache.cpp

@@ -287,6 +287,9 @@ RideCache::addRide(QString name, bool dosignal, bool select, bool useTempActivit
         // notify everyone to select the one we were already on
         context->notifyRideSelected(prior);
     }
+
+    // model estimates (lazy refresh)
+    estimator->refresh();
 }
 
 void
@@ -376,6 +379,9 @@ RideCache::removeCurrentRide()
 
     // now select another ride
     context->notifyRideSelected(select);
+
+    // model estimates (lazy refresh)
+    estimator->refresh();
 }
 
 // NOTE: