Cannot set keyboard focus to other sections in Mate Tweek

[Brandon Tyson]

Steps to Reproduce:

1. In Ubuntu Mate 17.10 or Ubuntu Mate 18.04 turn on the screen reader with super+alt+S.
2. Open Mate Tweek.
3. Visually, you will see several sections: "Desktop Icons", "Panels" and "Windows". Notice that keyboard focus lands in the "desktop icons" section.
4. Try to use the keyboard to switch sections.
Actual results: There is no way to switch to a different section to customize its settings.
Expected Result: The user can navigate to the list of sections and select a different section to change its corresponding settings.

The last version I used that this worked correctly in was 16.04 LTS.
This is important to me for two reasons:
1. Ubuntu Mate 18.04 LTS is a longterm support version, and these versions have always been really good about accessibility.
2. With the default panel layout being changed from "traditional" to "familiar" for new installations of Ubuntu Mate 18.04, at present there is no way to switch the panel layout if someone using the screen reader prefers the traditional option (it actually provides better keyboard accessibility than the "familiar" layout).

Thank you very much for your time and I look forward to any fixes you may be able to provide.

Sincerely,

Brandon Tyson

[Victor Kareh (vkareh)]

Upstream bug: https://github.com/ubuntu-mate/mate-tweak/issues/38