Create the concept of "page types" which let us specify the kind of
page that we're rendering in high level terms. Currently there are
three page types: album, photo and tag.
The tag page type uses slightly different variables. It has a $tag
but no $item. Adjust all sidebar_block() functions to avoid printing
stuff that's dependent on the item if there is no item.
Simplify the tag code to stop trying to fake an item.
Update the theme slightly to use $item and $tag where appropriate
(notably, for making the <title> element).
$theme->block_type() so that the themer has a consistent interface.
Also added a bunch more callbacks and normalized the names so that the
module author has plenty of options for where stuff gets put on the
page. Especially renamed album/photo/sidebar to be album_blocks()
photo_blocks() and sidebar_blocks() to make it clear that those are
going to be larger content sections and not just basic insertion
points.
Used __call() to collapse all functions in the theme, which
incidentally makes it trivially easy to add a new insertion point.
sidebar.html.php file loops over $theme->blocks() which in turn calls
carousel::block() which uses the Block object to create a standard
block UI. Hooray!
