feat: say when the system runs another version

The installer reads the version the system states in its own file,
without running anything: batocera.version, recalbox.version (a release
only), RetroBat's system/version.info, VERSION_ID in os-release on Lakka
and EmuELEC. When it differs from the version the list was built for, a
line says so before the install and again with the result, and the new
version event carries it for the screen. An unknown version says
nothing, and the install never stops on it.

install.sh

@@ -18,7 +18,7 @@ esac
 TEMP_INSTALLER=""
 TEMP_DIRECTORY=""
 DEFAULT_INSTALL_URL="https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-DEFAULT_INSTALL_SHA256="749d14547ad7a5504ff6ee4c62aca2ec710839174e149df77759c70d3e4fe951"
+DEFAULT_INSTALL_SHA256="8e6be38d489e9b481c8e82ba964b54054524b7a103a7527eddce20e52b261f0e"
 MAX_INSTALLER_BYTES=2097152
 
 cleanup() {