Fix severe simulation memory leaks

eeschema/sim/ngspice.cpp

@@ -680,4 +680,10 @@ void NGSPICE::validate()
 }
 
 
+void NGSPICE::Clean()
+{
+    Command( "destroy all" );
+}
+
+
 bool NGSPICE::m_initialized = false;

eeschema/sim/ngspice.h

@@ -93,6 +93,9 @@ public:
     ///< @copydoc SPICE_SIMULATOR::GetNetlist()
     virtual const std::string GetNetlist() const override;
 
+    ///< @copydoc SIMULATOR::Clean()
+    void Clean() override final;
+
 private:
     void init();
 

eeschema/sim/sim_plot_frame.cpp

@@ -480,6 +480,7 @@ void SIM_PLOT_FRAME::StartSimulation( const wxString& aSimCommand )
     m_simulator->LoadNetlist( formatter.GetString() );
     updateTuners();
     applyTuners();
+    m_simulator->Clean();
     m_simulator->Run();
 }
 
@@ -1649,6 +1650,8 @@ void SIM_PLOT_FRAME::doCloseWindow()
     if( m_simulator->IsRunning() )
         m_simulator->Stop();
 
+    m_simulator->Clean();
+
     // Cancel a running simProbe or simTune tool
     m_schematicFrame->GetToolManager()->RunAction( ACTIONS::cancelInteractive );
 

eeschema/sim/spice_simulator.h

@@ -91,6 +91,11 @@ public:
      */
     virtual bool IsRunning() = 0;
 
+    /**
+     * Clear simulation data (i.e. all vectors).
+     */
+    virtual void Clean() = 0;
+
     /**
      * Execute a Spice command as if it was typed into console.
      *