MWS: Logging into one browser/device also logs users out of other browsers/devices

[Jermolene]

Tested with commit e48ea2d

Steps to reproduce:

1. Take a fresh copy of the MWS repo at the commit above
2. Run npm install and npm start
3. In the primary browser, visit localhost:8080 and click the button to create an admin account
4. Observe that the primary browser is now logged in as the admin account
5. In the secondary browser, visit localhost:8080 and log in with the same admin account credentials
6. Observe that the secondary browser is now logged in as the admin account, but refreshing the primary browser shows that it has been logged out

I would expect to be able to log into multiple devices at the same time.

cc @webplusai