Zulip: Reduce size of user-info pop-up for screen width less than 600px

[Lplenka]

I was checking out the web-app's UI in my mobile.
Found this issue. The size of pop-up showing user info by clicking the user name should be reduced for mobile devices, especially for screen size less than 600px.

[timabbott]

I think it might be reasonable to just move where the popover appears to be more centered.

I guess while we're working on this responsiveness issue, we should also see if we can shrink the compose buttons area to fit in 1 line.

[zulipbot]

Hello @zulip/server-message-view members, this issue was labeled with the area: message view label, so you may want to check it out!

[brockwhittaker]

@zulipbot claim.