Add Insert method to Accordion

[JeffreyLeeLi]

Checklist

• I have searched the issue tracker for open issues that relate to the same feature, before opening a new one.
• This issue only relates to a single feature. I will open new issues for any other features.

Is your feature request related to a problem?

I'm frustrated to manipulate Items field directly, 'coz it'll panic.

Is it possible to construct a solution with the existing API?

None works for me now.

Describe the solution you'd like to see.

func (a *Accordion) Insert(index int, item *AccordionItem)

[Jacalz]

I'm not necessarily saying that I'm against adding this, but I want to clarify that "coz it'll panic" is not a good enough reason for adding this. As explained in the previous issue, it panics because of a race condition that that has very likely been fixed on the develop branch for 2.6.

[JeffreyLeeLi]

... it panics because of a race condition that that has very likely been fixed on the develop branch for 2.6.

OK. Good news to hear.

Thanks for the explanation.

And I'll wait for the version to release, then.