feat: add Region & Language page

[mmstick]

Closes #12

[git-f0x]

Might be a bit of an edge case, but I can't seem to set Serbian (Latin) as a language (it defaults to Cyrillic).
I think GNOME Settings on 22.04 provided such an option (maybe lichen doesn't support that yet?).

[git-f0x]

Sliders are also slightly broken for some reason. Not sure what libcosmic (or possibly iced) commit caused that.

[mmstick]

Yeah I've been looking into a similar issue with FlexRow's child widgets having the same width as the FlexRow widget.

[git-f0x]

The only somewhat notable change that could affect that between updates is the Iced update (which includes pop-os/iced@51ad918 and the commit after it).

[wash2]

Not sure why this would only now become a problem, but https://github.com/pop-os/libcosmic/blob/3dcc47d6a7d14423fbd372a0a5ce3c7c9581dd75/src/widget/flex_row/layout.rs#L66 seems to pass the limits of the flex row to each child widget. I guess it is recalculated afterward, so that may not be responsible.

[mmstick]

Narrowed it down to a change in libcosmic

[git-f0x]

Oh, I caused it. Sorry!
It previously wasn't in a container (before the 32px min height commit), so I thought it was unnecessary after the rebase changes.