Fixed crashes of ratsnest when a pointer for an item has changed after undo/redo operations.
Vias are properly removed from ratsnest (pcbnew/class_board.cpp).
RN_DATA::Update()/AddSimple() take BOARD_ITEM* as the parameter (instead of being split to versions with BOARD_CONNECTED_ITEM* and MODULE*), to make the code look clearer.
Modifications done using the EDIT_TOOL are saved using the default KiCad's undo buffer.
If there is only one item selected, info about the item is displayed in the bottom status bar.