fix(accordion): callbacks for closing exclusive accordions

[lubber-de]

Description

• Exclusive accordions only triggered the callback for the opening according but not for all the closing ones.
• Also added the ability to cancel any open/close by returning false from the onOpening/onclosing/onChanging callbacks

Testcase

https://jsfiddle.net/lubber/dmqpnLtu/9/

Closes

#2826

[lubber-de]

I put this on hold for now, as, after some investigation, the current logic would need more refactoring to support that properly and be consistent as "closeothers" behaves differently than just closing the active accordion.