Added new sidebar format. Ajax calls now make of proper types of requests.

Removed 'simple_sidebar' preference, replaced with 'sidebar_style'.

Added 'fancy' sidebar style, which hides some controls behind menus.

Added '?' keyboard command to toggle an ugly legend of keyboard commands.
Added 'r' keyboard command to refresh the sidebar.

Added fof_db_mark_tag_read() to remove unread tag from all items with some other tag.

Ajax calls which change server state now all use POST requests.  Also now use hash objects as request parameters, so that encoding is automatic.