stumble 5.x-1.1

• Major random node selection rewrite
• Added administration menu
• Stumbling can now be enabled for certain content types, not just everything
• Stumbling can also be restricted to the same content type. For example, a user on a story node will only stumble to more story nodes.
• #154386: Add "stumble" class to allow theming of the "Stumble" link (using an image)

NOTE: Before you actually see the 'Stumble' link below a node, you need to enable stumbling for a content type or two in the administration menu (admin/settings/stumble).