Blender Git Loki

UI: Improve node editor breadcrumbs display

This patch upgrades node editor breadcrumbs to have slightly more
visual weight, to including the base path of object/modifier/world,
etc, have more visually pleasing spacing, and contain icons.

In the code, a generic "context path" is added to interface code.
The idea is that this could be used to draw other breadcrumbs in areas
like the property editor or the spreadsheet, and features could be added
to all of those areas at the same time.

Ideally we would be able to control the color of the breadcrumbs with a
specific theme color, but since they are drawn with the regular layout
system, that is not easily possible.

Thanks to @fabian_schempp for the original patch.

Differential Revision: https://developer.blender.org/D10413