Add support for the "toc" chapters attribute

[mitchdowney]

Shared by John Spurlock on Podcast Index Social.

Turns out today we can easily see which apps implement the obscure json chapters "toc" attribute [1] properly.

"toc": false should hide a chapter from visual display (a "silent chapter")

If you see a single chapter called "Coming soon..." in your app for today's Podnews episode, your app supports json chapters (good) but doesn't support toc: false (bad), file a bug with them!

[1] https://github.com/Podcastindex-org/po

related to:
podverse/podverse-rn#1984
podverse/podverse-web#1201