Add app bar to main views

[alya]

At present, the four main views accessible via the bottom navigation buttons do not have an app bar. This makes it harder to figure out at a glance what you're looking at.

We should therefore add an app bar to these views, with the following headings:

1. Streams list: "Streams"
2. PMs list: "Private messages"
3. Status and settings menu: "Profile and settings"

The work to do this for Inbox is different, an is tracked separately as #5501.

CZO discussion thread

[suehirego]

I'm working on this issue and would like to claim it

[chrisbobbe]

Thanks, @suehirego! Please let us know what questions you have, here or on chat.zulip.org.

[kirtanlab]

I want to work on this @chrisbobbe

[kirtanlab]

actually which different components are needed at the top app bar? and what about existing components?