TDB2 Conversion

- Migrated several commands over to use TDB2.  Have to start somewhere.

src/TDB2.h

@@ -54,6 +54,7 @@ public:
   void add_line (const std::string&);
   void clear_lines ();
   void commit ();
+  void commitUndo ();
 
   void load_tasks ();
   void load_lines ();