[orca-list] Automatic focus mode as a result of structural navigation is now configurable

[Joanmarie Diggs <jdiggs igalia com>]

Hey all.

As the subject states, automatic triggering of focus mode as a result of
structural navigation is now configurable. Things to note:

* The default behavior is to trigger focus mode. The reason for this
  choice is that prior to this feature, that is what happened: Pressing
  'e' to move to an entry disabled structural navigation. So having
  it enabled by default makes the new user experience consistent with
  the old one and is less disruptive/confusing to novice users.

* The option has not yet been added to the GUI or the documentation.
  Again, until we sort all this stuff out, things are subject to change.
  But my plan is to make the final settings, once agreed upon, to the
  GUI. In the meantime:

* In order to disable automatic focus mode as a result of structural
  navigation, you must currently do so via your orca-customizations.py.
  These lines should work:

  import orca.settings
  orca.settings.structNavTriggersFocusMode = False

* Yes, I know we also need to do this for caret navigation. But there
  are some related caret navigation issues I'm still working out. Until
  I work them out, I'm not going to introduce a setting which you will
  tell me is broken because of the issues I've not yet worked out.
  <smiles>

Hope this option is of use to you. Please let me know what you think.
Thanks!

--joanie