themes & blocks - MDL-19077 & MDL-19010 blocks are now printed by the theme

themes & blocks - MDL-19077 & MDL-19010 blocks are now printed by the theme

The code to print blocks in now in theme layout.php files. (Or in
moodle_core_renderer::handle_legacy_theme)

Code for printing blocks everywhere else has been stripped out.
(Total diffstat 1225 insertions, 2019 deletions)

The way the HTML for a block instance is generated has been cleaned
up a lot. Now, the block_instance generates a block_contents
object which gives a structured representation of the block,
and then $OUTPUT->block builds all the HTML from that.

How theme config.php files specify the layout template and block
regions by page general type has been changed to be even more flexible.

Further refinement for how the theme and block code gets initialised.

Ability for scrits to add 'pretend blocks' to the page. That is,
things that look like blocks, but are not normal block_instances.
(Like the add a new block UI.)

Things that are still broken:
 * some pages in lesson, quiz and resource. I'm working on it.
 * lots of developer debug notices pointing out things that
   need to be updated.