Added "continuous logging" functionality.

This is useful if you're having stability troubles and/or are worried
about crashes. With traditional logging you can lose your capture if
the program, CAN adapter, or computer crash before you've saved. With
continuous logging the file is flushed to disk every couple of seconds
so you won't lose more than a few seconds of log even during a crash.

mainwindow.h

@@ -58,6 +58,7 @@ private slots:
     void handleSaveFilteredFile();
     void handleSaveFilters();
     void handleLoadFilters();
+    void handleContinousLogging();
     void showGraphingWindow();
     void showFrameDataAnalysis();
     void clearFrames();
@@ -132,6 +133,9 @@ private:
     bool bDirty; //have frames been added or subtracted since the last save/load?
     bool useFiltered; //should sub-windows use the unfiltered or filtered frames list?
 
+    bool continuousLogging;
+    int continuousLogFlushCounter;
+
     //References to other windows we can display
     GraphingWindow *graphingWindow;
     FrameInfoWindow *frameInfoWindow;