Allow expanding/collapsing items from keyboard in generic wxDVC

Add the usual handlers for '-', '+' and '*' keys. The last one is
especially convenient, as it does something that couldn't be easily done
at all interactively before.

src/generic/datavgen.cpp

@@ -4612,7 +4612,27 @@ void wxDataViewMainWindow::OnChar( wxKeyEvent &event )
         case WXK_DOWN:
             OnVerticalNavigation(event, +1);
             break;
-        // Add the process for tree expanding/collapsing
+
+        case '+':
+        case WXK_ADD:
+            Expand(m_currentRow);
+            break;
+
+        case '*':
+        case WXK_MULTIPLY:
+            if ( !IsExpanded(m_currentRow) )
+            {
+                Expand(m_currentRow, true /* recursively */);
+                break;
+            }
+            //else: fall through to Collapse()
+            wxFALLTHROUGH;
+
+        case '-':
+        case WXK_SUBTRACT:
+            Collapse(m_currentRow);
+            break;
+
         case WXK_LEFT:
             OnLeftKey(event);
             break;