Update glib.vapi to 0.26

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Add MP3 check backend

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Convert pipeline messages to signals

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Fix async message delivery and disposal

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Add MP3 format check GUI

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>