Pressing the "i" key makes button disappear (and other issues)

[chaosphere2112]

Fixes 3 issues I found while testing text in the GUI; one was difficult to write a test for, so I punted on it, one was just a plain-out error, and the third is now properly tested.

1. In certain circumstances, you could get an error message when stopping editing text, due to the manager of the widget having been del'd by detach. This has been fixed.
2. If you pressed "Escape" to stop editing a text box, it would turn to just a blank box. Fixed, and tested.
3. Pressing the "i" key would hide a random widget, and pressing it again would bring it back. Tracked down where in the VTK documentation it mentions something pertaining to that, turned off that feature for all widgets. Couldn't come up with a good way to recreate programmatically.

[chaosphere2112]

@aashish24 @doutriaux1

[doutriaux1]

348: Test command: /lgm/uvcdat/2.2.0-rc1/bin/python "/git/uvcdat/testing/vcs/vtk_ui/test_vtk_ui_textbox_blank_test.py"
348: Test timeout computed to be: 1500
348: /lgm/uvcdat/2.2.0-rc1/bin/python: can't open file '/git/uvcdat/testing/vcs/vtk_ui/test_vtk_ui_textbox_blank_test.py': [Errno 2] No such file or directory
1/1 Test #348: test_vtk_ui_textbox_blank_text ...***Failed    0.02 sec

forgot to add the file?

[chaosphere2112]

@doutriaux1 Nope, I typo'd. Should be blank_text. I'll update.

[chaosphere2112]

@doutriaux1 Should be fixed now

[aashish24]

will have a look at it today..

[doutriaux1]

ok tests pass for me, merging