Fix breadcrumb rendering for all themes.
Allow themes to override breadcrumbs colors (background, text)

Change nemo-supplied style sheet to fallback.

Need to rework sidebar disk full renderers to accomodate change
Split up style files into those that can be overridden by themes,
and those that cannot.
Allow theme to determine border color of breadcrumbs.
Breadcrumbs: allow theme control of border-radius
Fix radius
Add initial style name.
Adjust breadcrumb draw box a little bit, to make left end button
a bit more well-defined
Use more widely-used theme color names for breadcrumbs styles
Add to NEWS info about themeing breadcrumbs.
Merge pull request #188 from mtwebster/breadcrumbs-themes-suck

Fix breadcrumb rendering for all themes.