Add the collapse feature.

[luyilin]

Add a collapse prop to indicate a collapsible element.
In this component it only can be set to TimelineTitle, as the collapsible element must has a child element.

[mayashavin]

@luyilin I will work on this. Please assign it to me :)

[luyilin]

assigned to @mayashavin manually, have no idea why I cannot assign to you in this page 😅

[mayashavin]

@luyilin if you want, you can add me as collaborators and then you can assign me 😄 Below is how to do that
https://help.github.com/articles/inviting-collaborators-to-a-personal-repository/

[luyilin]

I have sent an email invitaion to you. ☺️