This uses applySnapshot to update the class users in place.
This will make code using these users more efficient since they can just observer the user properties for changes.

Original the MST environment was avoided because I was planning to
switch this store to just be MobX. However the group store needs to
be synced with the data from the database, and it is easier to do that
using MST than MobX.

This uses applySnapshot to sync the changes from the DB. This way the existing objects are updated instead of creating new ones.

I also missed a change in stores when committing the last set of changes.

This will allow us to update the users later and have the group views automatically update without having to also update the group user objects.

This also removes the option to skip unknown students. They are part of the group so we should show them even if we don't know who they are yet.

We use a timestamp for when the class information is retrieved from the portal. And compare this to the timestamp in the groupUser to figure out if this groupUser is older than the class info or newer than the class info.

The portal service object provides a place to store portal info like JWTs, and methods that use and update this info.

This new object is used to refresh the class info if necessary after updating the group info from Firebase.