Code review comment for lp:~azzar1/ubuntu-release-upgrader/fix-1799310

> Thanks for your work, one question. The design image on
> https://wiki.ubuntu.com/ReleaseUpgrades has a settings button on the bottom
> left corner, is that omitted on purpose in the implementation? (if so maybe
> add a comment stating why?)

The main reasons are:
- atm there is no way to ask software-properties-gtk to open the livepatch tab. We can open tab by numbers and not by name. Considering that we're moving around tabs, using the number is not a good solution.
- I want to keep the diff as small as possible. In particualar I had to add a mechanism to show that button only under Gtk3. Considering the controller/view model of ubuntu-release-upgrader it's not naive as it seems.

Considering these mpt agreed to not show the button for the moment.