Undo: implement undo of depth and duration editing

This was a bit different from the other editing commands:
1) Only the current dive is edited not all selected dives.
   Therefore, create a function that turns the current dive
   into a one-element list.
2) The profile has to be replot. Here, likewise, create a
   function to do that.

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

core/subsurface-qt/DiveListNotifier.h

@@ -14,6 +14,8 @@
 // Use "enum class" to not polute the global name space.
 enum class DiveField {
 	DATETIME,
+	DEPTH,
+	DURATION,
 	AIR_TEMP,
 	WATER_TEMP,
 	DIVESITE,