Can't log in when file open

[curran]

As a user who just attempted to edit their own viz while not logged in, I want to log in, so that I can edit the viz.

Current behavior:

• I need to close all the files and the sidebar in order to see the log in button

Desired behavior:

• Logging in should be one click away in this case

Similar to https://github.com/vizhub-core/vizhub-feedback/issues/779

[curran]

Maybe the top bar should only hide if you're logged in...

[curran]

Done! Now the top bar only hides if the user is logged in.