Remove glade reference

There's no reason to keep the "generated by glade version x" in the UI
files. Remove it.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Remove status bar's margin_start and margin_end

The application emits a warning on launch that these proprieties are
unknown. Remove them.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>