Attempt at a clearer example of data channels

[corranwebster]

This bundles country info into an object that contains name and flag information with a custom value type that handles it.

Hopefully this example makes clearer the idea that an item in a model may be more complex than just a scalar value and may have multiple linked data channels.

This is a draft, because it may make sense to bundle this example in with the EnumType PR in some way.

[corranwebster]

Suggested change

	country = Instance(Country, allow_none=True)
	country = Instance(Country, allow_none=False)

D'oh!

[codecov-io]

Codecov Report

Merging #785 into master will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #785      +/-   ##
==========================================
+ Coverage   40.81%   40.88%   +0.07%     
==========================================
  Files         508      508              
  Lines       27832    27832              
  Branches     4217     4217              
==========================================
+ Hits        11359    11379      +20     
+ Misses      15992    15979      -13     
+ Partials      481      474       -7     

Impacted Files	Coverage Δ
pyface/ui/wx/data_view/data_view_model.py	56.14% <0.00%> (-1.76%)	⬇️
pyface/ui/qt4/console/console_widget.py	29.28% <0.00%> (+0.20%)	⬆️
pyface/ui/qt4/code_editor/code_widget.py	44.39% <0.00%> (+0.84%)	⬆️
pyface/wx/python_stc.py	10.36% <0.00%> (+1.21%)	⬆️
pyface/ui/wx/window.py	77.10% <0.00%> (+2.40%)	⬆️
pyface/ui/qt4/util/gui_test_assistant.py	80.53% <0.00%> (+2.65%)	⬆️
pyface/ui/wx/data_view/data_view_widget.py	77.52% <0.00%> (+5.61%)	⬆️
pyface/__init__.py	88.88% <0.00%> (+7.40%)	⬆️
pyface/i_file_dialog.py	84.61% <0.00%> (+7.69%)	⬆️

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