Added BOUNDING BOX selection of multiple widgets on the dialogs by left clicking...

Added BOUNDING BOX selection of multiple widgets on the dialogs by left clicking and dragging the mouse while holding down the left mouse button to draw a rectangle around the widgets to be selected
Added code to the popup menus to identify which widget/dialog was right clicked
Double clicking an item in the TREE pane will bring up the EDIT PROPERTIES dialog for the widget/dialog that was double clicked.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@8974 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775