Errors in doc examples

This issue relates to the example code found in
tutorials - https://github.com/enthought/traitsui/tree/master/examples
(a sub-issue of #1027 )

- [x] When I run the tree_editor.py file everything runs fine, but if I click on an employees name, and then click in any textbox I get the error:
```
$ python tree_editor.py
Traceback (most recent call last):
File "/Users/aayres/.edm/envs/general-use/lib/python3.6/site-packages/traitsui/qt4/ui_panel.py", line 338, in sizeHint
if ui.view.width > 0:
AttributeError: 'NoneType' object has no attribute 'width'
Abort trap: 6
```

- [ ] Also, there is a bit of mismatch between the code files in this directory, and the examples given in the traitsui user manual.
Example 1 in the manual explicitly references a file configure_traits.py which does not exist in the directory. Similarly examples 5b references default_traits_view2.py which is not in the directory. Additionally, the directory contains files view_standalone.py, view_multi_object.py, view_attributes.py, and include_extra.py which are not mentioned in the user manual.

- [ ] I noticed that in the user manual the example numbers randomly jump from 9 to 12 (there is no example 10 or 11).

- [x] In example 15 in the manual the last line of code from the file enum_editor.py is missing.

- [x] Additionally, some docstrings for files don't line up with the intended new content being shown by that example.

- [x] Finally, when running the tutor.py file I see a variety of errors and the application gets hung frequently

------EDIT-------
The previously listed errors referencing the strange command line debug output have been moved to a new separate issue #1061