Update Moodle to 2.4.8 version

View version changelog on:
- http://docs.moodle.org/dev/Moodle_2.4.8_release_notes
- http://docs.moodle.org/dev/Moodle_2.4.7_release_notes
- http://docs.moodle.org/dev/Moodle_2.4.6_release_notes
- http://docs.moodle.org/dev/Moodle_2.4.5_release_notes
- http://docs.moodle.org/dev/Moodle_2.4.4_release_notes