Solve latecomer problem with the activity (latecomers don't get the activity)

[cbradyatinquire]

When a student joins the activity late (or when a teacher joins a group already in progress through the View menu, they should get the activity and its current state).

[cbradyatinquire]

The test for showing this issue is...

1. Teacher starts an activity
2. Student joins a group THAT HAS NO ONE ELSE IN IT.

The student will not get the activity in this case.

If the student joins a group that DOES have another student, then they will get caught up.

[cbradyatinquire]

Tested on Test (one machine, though - will be good to confirm in next classroom test).