Frontend for multiuse invites

I am working on the frontend part for multiuse invites. Multiuse invites are a link that a user can generate to invite other people to Zulip. One of my task before I get started with the it is to de-clutter invite modal in Zulip. To get started with that, first I have to change the “Streams they should join” part to just show a list with [Edit] option. When user clicks on [Edit], it should just show the current checkbox scheme.

This is how it is currently shown.

This is how it will be once my PR gets merged. This is a simpler and cleaner design.

I have raised a pull request for this. Once it gets merged, I will work on making the design of the invite modal more vertically aligned. By vertically aligned, I mean something like this:

Emails (one on each line or comma-separated)
[box for emails]

Users join as 
o Regular users
o Administrators (this will be made nicer in #7690)
 
   --- OR ---

Get an invite link to share


Initial streams
Users will start in #stream1, #stream2, #stream3 [Edit]

This is all for now.