Improved keyboard navigation support

[mmstick]

• The return key will now select the active option and move to the next view / variant list box.
• The backspace and return keys will logically move backwards to the previous view / unset the variant list box

Closes #279
Closes #280

I'm going to keep adding onto this for a bit longer.

Requires #340 to fix an issue with unsetting the variant

[tintou]

I'm unsure that we want to give this meaning to backspace, we never did and I wonder if it will work properly with entries (untested here)…

[tintou]

But otherwise, good move :)

[mmstick]

@tintou Yes, backspace it still works with entries.

[danirabbit]

I'm -1 on introduce backspace as a navigation shortcut. We've had this discussion several times in other apps and we always decide that it's a bad idea. Even the major browsers are moving away from this shortcut. Instead, the standard back navigation shortcut is alt + ←

[mmstick]

@danrabbit I'll start working on fixing the issues you pointed out. Shouldn't take long.

[danirabbit]

For the back button shortcut we should be using GLib.Action and action accelerators. Manually listening to key press events always gets us in trouble with layouts and such.

For the most part, I don't think it's a good idea to manually grab the enter key. It would probably be better to use the activation signal from the listbox

[cassidyjames]

This seems a little all over the place. Manually listening to all of these key events seems unnecessary, especially since Gtk handles a lot of this for us with focus. I'm also concerned with the affects on keyboard navigability to select and activate widgets other than the next/back buttons in this case.

If we are adding effectively global key events, we should be using GLib.Action for the shortcuts. But perhaps a better route is ensuring widgets are properly focused when the views are loaded, and the widgets properly activate defaults?

[danirabbit]

Gonna close this since there's not been any movement in quite a few months

[mmstick]

@danrabbit Feel free to close all of them. They're vastly outdated compared to our current work, as seen in pop-os#173. Some views have been rewritten.