MDL-49684 timezones: rewrite timezone support

This patch replaces all homegrown timezone
stuff with standard PHP date/time code.

The main change is the introduction of core_date
class that returns normalised user and server
timezones. From now on nobody should be using
$CFG->timezone or $user->timezone directly!

Other new features and fixes:
* admins are prompted for timezone during install
* editing of other users is finally fixed
* timezones are displayed in user profile
* new $this->setTimezone() in phpunit
* time locale is now automatically reset in phpunit
* timezone is now automatically reset in phpunit
* phpunit has Australia/Perth as default timezone

lib/phpunit/classes/advanced_testcase.php

@@ -501,6 +501,19 @@ abstract class advanced_testcase extends PHPUnit_Framework_TestCase {
         self::setUser(1);
     }
 
+    /**
+     * Change server and default php timezones.
+     *
+     * @param string $servertimezone timezone to set in $CFG->timezone (not validated)
+     * @param string $defaultphptimezone timezone to fake default php timezone (must be valid)
+     */
+    public static function setTimezone($servertimezone = 'Australia/Perth', $defaultphptimezone = 'Australia/Perth') {
+        global $CFG;
+        $CFG->timezone = $servertimezone;
+        core_date::phpunit_override_default_php_timezone($defaultphptimezone);
+        core_date::set_default_server_timezone();
+    }
+
     /**
      * Get data generator
      * @static