Show current organization's name and icon atop main menu

[gnprice]

This is a followup to:

• Bottom tabs and main menu #1035

As the design in Figma shows, we'd like the main menu to identify the current organization, using its name and icon:

To do that, we'll need to track the realm name and realm icon in our data model. For this issue, though, we don't need it in the persistent database — so we get to skip the full complexity of #1036. Instead we just need to have the values on PerAccountStore, and keep them updated there.

[sand-storm-17]

Hi, I've started working on this issue and would like to claim it

[PIG208]

Welcome @sand-storm-17, this is a follow-up after #1035 is resolved. Until then, I would recommend looking at some other issues to work on. Please take a look at our documentation on Picking an issue to work on to get started.