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).
1) We now use __call() in REST_Controller to handle any requests to a controller
that were not already handled. In the case of RESTful controllers, this should
be the only entry point (although they're free to break the model and add other
ones.. nothing stops them).
This means that we can remove all the catch-all routes in
routes.php which greatly simplifies it.
2) Move request_method() and output_format() out of REST_Controller and into the REST
helper in core/helpers/rest.php
3) Experiment with letting the various subclasses check the output_format and deal with
it themselves. This simplifies the API, but it might be a bad idea in that it might
push too much work to the individual controllers. It's a balancing act, time will tell,
I'm willing to change it back later.
