[apps/probability] Implement reset of snapshot

Change-Id: I180915a255f45930b407743b9c43e55c2723e1a1

apps/probability/app.cpp

@@ -42,6 +42,14 @@ App::Descriptor * App::Snapshot::descriptor() {
   return &descriptor;
 }
 
+void App::Snapshot::reset() {
+  law()->~Law();
+  new(m_law) BinomialLaw();
+  calculation()->~Calculation();
+  new(m_calculation) LeftIntegralCalculation();
+  m_activePage = Page::Law;
+}
+
 Law * App::Snapshot::law() {
   return (Law *)m_law;
 }

apps/probability/app.h

@@ -41,6 +41,7 @@ public:
     ~Snapshot();
     App * unpack(Container * container) override;
     Descriptor * descriptor() override;
+    void reset() override;
     Law * law();
     Calculation * calculation();
     Page activePage();