Turn Calculator into a singletome and move the list of timesteps inside calculator.

library/include/mobilisis/calculator_functions.h

@@ -13,9 +13,23 @@
 using namespace std;
 
 class Calculator {
-public:
+    mutable QList<int> m_timeSteps;
+
+protected:
     explicit Calculator() = default;
 
+public:
+    Calculator(Calculator const &other) = delete;
+    void operator=(Calculator const &) = delete;
+
+    static Calculator &GetInstance() {
+        static Calculator c;
+        return c;
+    }
+
+    void ResetTimeSteps() { m_timeSteps.clear(); }
+    QList<int> timeSteps() const { return m_timeSteps; }
+
 	/// <summary>
 	/// Gets duration in seconds from cost
 	/// </summary>