[aps/solver] Reset the solution selection when leaving the view

Solve an equation that has solutions, select a solution, then go back
and change the equation. WHen you go to the solutions, the previous
solution is still selected, which is a little weird

apps/solver/solutions_controller.h

@@ -17,6 +17,7 @@ public:
   const char * title() override;
   View * view() override { return &m_contentView; }
   void viewWillAppear() override;
+  void viewDidDisappear() override;
   void didEnterResponderChain(Responder * previousFirstResponder) override;
   /* AlternateEmptyViewDefaultDelegate */
   bool isEmpty() const override;