xkb layouts are translated fine by libgnome-desktop. If not
we should go fixing there since that makes keyboard layout
strings consistent with e.g. gnome-control-center.
There weren't any 'exotic' strings in the current translations
so what we get from libgnome-desktop should be just fine.
In order to do that, an additional piece of state (layout switcher) was exposed to the event handlers, a separation between squeekboard-only and system layouts was introduced, along with a Translation structure to prevent mixing up strings.
Pulled in some Unix-specific code from https://github.com/rust-locale/locale_config to reduce dependencies.
First reason to reduce dependencies: gettext-rs is not in Debian. Copying gettext-sys might have made sense, but the interface is somewhat confusing.
For translating a couple identifiers, detection and some hand-rolled hash map is all that is needed, and the option to move to gettext later remains.
locale_config has been stripped of the lazy_static dependency, which, messing with the strtup sequence, might be a source of debugging woes. Plus setting language once in the beginning is somewhat inflexible regarding runtime changes.
