Add Short Name for Categories and add theme option(s) for categories in the navigation bar

There's been several requests (and hacks) for having the category trail in the breadcrumb trail. Now that categories have a proper edit screen this is potentially much easier. My proposal:

• Add an additional (required?) field to the categories table - short name. (Need to think about what to do to fill the field initially, or perhaps just use the long one if no short)
• Add an option in theme settings to extend the breadcrumb. I would have three options, 'off',' top category only', 'all categories'. Or perhaps just the category depth to display.