[orca-list] New spell-check support added

[Joanmarie Diggs <jdiggs igalia com>]

Hey all.

I have just committed a change to master designed to get Orca's
presentation of spell-check dialogs working again -- and working
consistently regardless of the app you are using. This support has been
implemented so far for Gedit and Thunderbird. Here's how it works:

By default, given a misspelled word in a supported spell-check dialog,
Orca will:

1. Speak the error/misspelled word
2. Spell the error/misspelled word (this can be turned off)
3. Speak the suggestion
4. Spell the suggestion (this can be turned off)
5. Present the context (this can be turned off)

Once you make a choice (Ignore, change, etc.) and the new error is
presented, Orca should do the above for the new error automatically.

In addition:

1. Basic where am I will present/repeat the above adhering to your
   settings. This is to handle the "I didn't catch that" situation.
2. Detailed where am I will present the above and will override your
   "normal"/default spellcheck settings. This is for people who
   normally don't want anything spelled out or context provided --
   except for on rare occasions when they do.

As for other apps: I plan to make this change for Evolution and
LibreOffice, but the thing is: Evolution is generally inaccessible. And
LibreOffice's spellcheck has broken accessibility
(https://bugs.freedesktop.org/show_bug.cgi?id=74242). So I focused on
two apps that are accessible and which have accessible spell checkers so
you could test that while I work on other stuff. Please let me know what
you think.

Thanks!
--joanie