Configurable node types

[ShadowCross]

This commit includes the following:

1. Allow user to configure which node types to include in the Sitemap via the admin Settings (Extensions > Sitemap > Options. The settings value is a comma-separated list of Content types (using the "alias"). When setting up several Croogo-based websites, I created new Content types so that the non-tech-savvy administrators can easily enable/disable parts of special lists (i.e. staff/board member lists, testimonials, etc.) which I didn't want to include as separate entries in the Sitemap.
2. Minor change for compatibility with the current 1.3 branch of Croogo. When deactivating the plugin, use the new hook system/method.

[ShadowCross]

Sorry, I forgot to update the label on the Extensions > Sitemap > Options page. In addition, a subsequent commit adds a configurable sort order -- the value can be

• Node.id (sorted in the order the nodes were saved)
• Node.lft (sorted in "tree" order)
• Node.title (sorted alphabetically)

and can have " DESC" at the end of the value to reverse the order.