core: add constructor/destructor pairs to dive and divecomputer

This allows us to use non-C member variables. Convert a number
of pointers to unique_ptr<>s.

Code in uemis-downloader.cpp had to be refactored, because
it mixed owning and non-owning pointers. Mad.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

desktop-widgets/profilewidget.h

@@ -48,7 +48,7 @@ private:
 	void editDive();
 	void exitEditMode();
 	void rotateDC(int dir);
-	OwningDivePtr editedDive;
+	std::unique_ptr<dive> editedDive;
 	bool placingCommand;
 };