Add ability to replan a dive that we planned before

When doing this, all waypoints of the calculated ascent are now waypoints
in the plan - so the user has to remove the ascent part of the dive in
order to really replan the dive. That's a pain, but we don't keep the data
around that would tell us which waypoints are user input and which ones
were calculated.

Fixes #527

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

qt-ui/mainwindow.h

@@ -118,6 +118,7 @@ slots:
 	void on_actionAboutSubsurface_triggered();
 	void on_actionUserManual_triggered();
 	void on_actionDivePlanner_triggered();
+	void on_actionReplanDive_triggered();
 	void on_action_Check_for_Updates_triggered();
 
 	void current_dive_changed(int divenr);