Segments inherit from Button and let us add clickable widgets
to status bars. This patch also adds proportional, fixed and
autosized modes for segments and lets the status bar consume
all non-clickable segments for override text.
Now that the GML formatter is both perserving comments and also mostly
agrees to the existing GML style, it can be used to auto-format all the
GML files in the system. This commit does not only contain the scripts
for running the formatting on CI and the pre-commit hook, but also
initially formats all the existing GML files so that the hook is
successfull.
