Describe the bug

g.gui.example module does not work. Probably already for a long time. There are multiple reasons why:

• some instructions in doc/gui/wxpython/example/README on how to modify Makefile are missing and some are outdated
• ExampleMapDialog.dataSizer.Add() has no argument item
• ExampleInfoTextManager.textCtrl has no method SetDefaultStyle
• dict.iteritems does not exist in Py3
• Example*Toolbar._getToolbarData() uses wrong syntax

To Reproduce

Start g.gui.example.

Expected behavior

g.gui.example works.