core: remove obsolte GTK3 type init call

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
core: add help text

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
css: project label markup change

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
css: change button style

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
css: do not define button in notebook style

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