#142 - Merged sitemap API

Also ID selection for the main_content block should work from the single site tree, when it's developed. So you don't select content-type+ID, you just browse to the content.

See if we can incorporate breadcrumbs into this, so they are auto-generated by the Site Tree where possible. Also tie in the logic about menu item subordination.

We don't need to see the term "entry point" anywhere in the UI or documentation. We can just use the term page-link.

Suggest that tracker item 415 also be addressed at the same time.
http://compo.sr/tracker/view.php?id=415

This functionality may be built on top of the new Resource-FS.

Note that we want to make sure that Comcode page hierarchy comes out of this system correctly. Currently the pages come out flat, because they are top-level under a zone.

We can also likely merge in the do_next_menu hooks as part of the site-tree, (and give site-tree nodes support for icons in the process).

Also consider if we need to allow different XML sitemaps, per content-type (i.e. to stop the main one getting larger than is allowed, isolating size problems in a specific sitemap).

Absorb the bookmarks menu into the site-tree also.

Also features like list_galleries, which are of very limited use, can simply become part of the new site tree.