1. Add missing _super calls.
2. Make UI widget destroys more consistent to avoid exceptions.
Selectable would throw an exception in the GridField.js if destroy
called from onunmatch - at that stage jQuery UI would have had called
the destroy already. Add a guard, and change to onremove, which triggers
before the element is removed from DOM.
3. DOM traversal fails after the element is removed from DOM.
Onunmatch triggers after the removal of the element from the DOM, which
makes DOM traversal fail. Use onremove instead, which triggers while the
element is still in DOM.
The accordion widget was previously being passed true and false, where as it either expects true or the integer of the panel to show.
This fix sets it as either false or 0.
* Use jquery ui accordion for the field, and implemented an admin theme.
* Made the setting of configuration consistent with other form fields.
* ToggleComposteField->startClosed() has been deprecated in favour of
setStartClosed().
* Removed public access to the heading level, instead use getHeadingLevel()
or setHeadingLevel().
API CHANGE Removed several unsed JavaScript globals: sprintf(), Number.prototype.CURRENCIES, Number.prototype.toCurrency(), String.prototype.ucfirst(), jQuery.fn.clearFields(), jQuery.fn.clearInputs()
MINOR Removed prototype_improvements.js and jquery_improvements.js files, now contained in individual component code (or removed altogether)
