module: replace deprecated gtk3 function

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
core: restructure module panel

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
core: restructure module panel

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
css: remove unrequired statements

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>