Styling for level navbar

Currently navbar_devel does not style the link elements ideally.

Vertical:

Horizontal:

I looked at how environment_indicator does it and have based a patch on their solution.

Vertical:

Horziontal:

I believe the patch can be used as-is but see the following future improvements:

• The reuse of the cog icon is not ideal and a unique icon should preferably be used later on.
• The level menu is very long, ideally this would be subdivided into more levels to allow for using the third level drop-down but that would ideally be done at devel's side, to not hardcode that menu reordering.
• There appears to be a small padding issue at the vertical top, I have not looked into this.