themes: MDL-19077 change how the theme is initialised and CSS is served.
This is part of http://docs.moodle.org/en/Development:Theme_engines_for_Moodle%3F $THEME is now initialised at the same time as $OUTPUT. Old functions like theme_setup are deprecated in favour of methods on $PAGE. There is a new theme_config class in outputlib.php that deals with loading the theme config.php file. CSS used to be served by themes styles.php files calling a function in weblib.php. Now it works by each theme's styles.php file doing $themename = basename(dirname(__FILE__)); require_once(dirname(__FILE__) . '/../../theme/styles.php'); which is less code to be copied into each theme. (Old-style styles.php files still work thanks to some code in deprecatedlib.php.) Admin UI for choosing a theme cleaned up. A couple of theme-specific hard-coded hacks like $THEME->cssconstants and $THEME->CSSEdit have been replaced by a more generic $THEME->customcssoutputfunction hook. See examples at the end of outputlib.php Also: * Fix setting the theme in the URL, which seems to have been broken since 1.9. * Fix up errors on a few pages caused by the new initialisation order. * MDL-19097 moodle_page::set_course should not set $COURSE unless it is $PAGE. * httpsrequired() from moodlelib.php moved to $PAGE->https_required(). * Move has_started() method to the renderer base class. * Further fixes to display of early errors. * Remove print_header/footer_old from weblib. I did not mean to commit them before.