gui: main window infrastructure

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
gui: finish main executer layout

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

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
css: style progress bar (needs further work)

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