Make sure all trait listeners get unhoooked

[aaronayres35]

ref: #870

There are some cases where we set up trait listeners but never ultimately unhook them (i.e. we never call .observe(_____, remove=True)). In many of these cases the use of the code is transient (e.g. examples / tests), but in any case it is best to always be safe. Any code which isn't transient this is very important as it could lead to strange bugs.

[aaronayres35]

Here is a list of observers I have found that do not appear to get unhooked (it is possible some items in this list may not actually require any change):

pyface/pyface/action/field_action.py

Line 52 in 05eefd4

field.observe(self.value_updated, "value")

pyface/pyface/dock/dock_window.py

Line 429 in 05eefd4

fb.observe(self._feature_bar_closed, "completed")

pyface/pyface/tasks/action/task_toggle_group.py

Line 119 in 05eefd4

self.window.observe(self._rebuild, "tasks.items")

pyface/pyface/ui/qt4/action/tool_bar_manager.py

Line 139 in 05eefd4

group.observe(

pyface/pyface/ui/qt4/wizard/wizard_page.py

Line 120 in 05eefd4

page.observe(self._on_complete_changed, "complete")

https://github.com/enthought/pyface/blob/master/pyface/ui/qt4/workbench/workbench_window_layout.py

pyface/pyface/ui/wx/expandable_panel.py

Line 129 in 05eefd4

heading.observe(self._on_button, "panel_expanded")

https://github.com/enthought/pyface/blob/master/pyface/ui/wx/action/tool_bar_manager.py

pyface/pyface/ui/wx/preference/preference_dialog.py

Line 137 in 05eefd4

tree_viewer.observe(self._on_selection_changed, "selection")

pyface/pyface/ui/wx/viewer/table_viewer.py

Line 96 in 05eefd4

self.observe(self._on_input_changed, "input")

https://github.com/enthought/pyface/blob/master/pyface/ui/wx/workbench/workbench_window_layout.py

pyface/pyface/wizard/i_wizard.py

Line 126 in 05eefd4

controller.observe(self._on_current_page_changed, "current_page")

pyface/pyface/workbench/workbench.py

Lines 134 to 138 in 05eefd4

	window.observe(self._on_window_activated, "activated")
	window.observe(self._on_window_opening, "opening")
	window.observe(self._on_window_opened, "opened")
	window.observe(self._on_window_closing, "closing")
	window.observe(self._on_window_closed, "closed")

pyface/pyface/wx/lazy_switcher.py

Line 64 in 05eefd4

model.observe(self._on_selected_changed, "selected")

https://github.com/enthought/pyface/blob/master/pyface/wx/switcher.py

pyface/pyface/wx/grid/grid.py

Line 57 in 05eefd4

model.observe(self._on_model_changed, "model_changed")

in tests: (probably can just add a tearDown method where we unhook things)
https://github.com/enthought/pyface/blob/master/pyface/data_view/data_models/tests/test_data_accessors.py
https://github.com/enthought/pyface/blob/master/pyface/tasks/tests/test_tasks_application.py
https://github.com/enthought/pyface/blob/master/pyface/tests/test_application.py
https://github.com/enthought/pyface/blob/master/pyface/tests/test_gui_application.py
https://github.com/enthought/pyface/blob/master/pyface/timer/tests/test_timer.py
https://github.com/enthought/pyface/blob/master/pyface/ui/qt4/tests/test_gui.py