Make streams expandable/collapsible in Streams panel

[alya]

In preparation for the mobile app redesign, we should implement the following functionality for the Streams panel:

1. Each stream should be expandable/collapsible within the panel, similarly to Make streams collapsible in inbox view #5423. Clicking on the stream name should expand/collapse it.
2. When a stream is expanded, we should use the logic used in the left sidebar of the webapp to decide how many topics to show.
3. An expanded stream should have a "more topics" link at the bottom. Clicking on this link should take the user to the full-screen topics list for that stream (currently accessed via the three bulleted lines icon in the stream header bar).

Note that unlike the left sidebar of the webapp, it should be possible to have several streams in the expanded state.

Design direction (visual redesign will be a separate follow-up issue):

[daleshort]

I don't know if I'm at the point of claiming this yet but I've been looking at it.

[daleshort]

I've made some progress on this and I'm ready to claim it assuming completing a PR in the next week or two would be ok.

[alya]

Sound great! Assigning the issue to you.

[alya]

Note that we have related work on #5423 / #5467 that might be a helpful starting point.

[dizzyjaguar]

I believe the changes in pull request #5467 should cover the collapsible part. It includes a prop that will make the StreamItem collapsible if desired. The only thing missing that doesn't overlap the two issues is the SHOW MORE TOPICS button and passing the collapsible prop in the Streams screen/adding the state.

[daleshort]

Looking for some guidance but I'll move that to the chat here: https://chat.zulip.org/#narrow/stream/48-mobile/topic/Collapsible.20Streams/near/1454210