"Followed" and "All topics" filters on inbox page

[gnprice]

The web app has the following feature:
https://zulip.com/help/inbox#filter-by-topic-status

you can control whether the Inbox includes all topics, just unmuted topics, or only topics you follow.

We should add a similar option to the inbox in the mobile app.

[gnprice]

Requested by a user recently: #feedback > feature request: mobile inbox/recent filters