Dive list: implement proper Qt-model semantics for DiveTripModel

Previously, each dive-list modifying function would lead to a
full model reset. Instead, implement proper Qt-model semantics
using beginInsertRows()/endInsertRows(), beginRemoveRows()/
endRemoveRows(), dataChange().

To do so, a DiveListNotifer singleton is generatated, which
broadcasts all changes to the dive-list. Signals are sent by
the commands and received by the DiveTripModel. Signals are
batched by dive-trip. This seems to be an adequate compromise
for the two kinds of list-views (tree and list). In the common
usecase mostly dives of a single trip are affected.

Thus, batching of dives is performed in two positions:
- At command-level to batch by trip
- In DiveTripModel to feed batches of contiguous elements
  to Qt's begin*/end*-functions.

This is conceptually simple, but rather complex code. To avoid
repetition of complex loops, the batching is implemented in
templated-functions, which are passed lambda-functions, which
are called for each batch.

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

desktop-widgets/simplewidgets.cpp

@@ -172,9 +172,6 @@ void RenumberDialog::buttonClicked(QAbstractButton *button)
 			}
 		}
 		Command::renumberDives(renumberedDives);
-
-		mark_divelist_changed(true);
-		MainWindow::instance()->dive_list()->restoreSelection();
 	}
 }