Fixes some minor bits:
- Fixed Essential theme overriding toggle text colour - see: https://moodle.org/mod/forum/discuss.php?d=251951.
- Fixed bullet point styles - see: https://moodle.org/mod/forum/discuss.php?d=251944.
- Refactored 'print_single_section_page()' in 'renderer.php' to call parent version of method and thus reduce code duplication and maintenance.
- Removed duplicate section title when editing.
As there is not enough time left in the universe to test to ensure that CT will never fail, please report issues with as much detail as possible even if it seems trivial. The 'Essential' issue is a third party theme and hence as I only test with core would not have been picked up. It would be impossible for me to test with all possible contributed plugin combinations.