* Use the 'starts with' selector when matching toggle groups by name in
non-exact mode to avoid potential conflicts with other toggle groups.
* Note down the required data attributes for JS in the template
documentations.
* Add a note of this output component in upgrade.txt.
* Add doc blocks for the core/checkbox-toggleall attributes and methods.
For cleaner templates, split checkbox toggle-all elements into three
templates:
* master checkbox (master control rendered as a checkbox)
* master button (master control rendered as a button)
* slave checkbox
