Clean up class summaries before new implementations

[patudom]

• ignore all student who use default measurements (handled by Add endpoint to set student's ignored status #187 / Add method to API handler for ignoring student cosmicds#394 / Adjust how shortcut buttons handle measurements hubbleds#1000)
• filter by minimum number of hubble measurements that remain; should be at least 75 (rather than 15 students who might be missing measurements) (to be consistent with what "small" vs "not small" class conditions) (done in Adjust class data filter #189)
• Any class that is empty should get deleted
• In class table, check if we use the flag test for anything - if not, delete the flag.
• In class table, add a flag real_class - if 1, it's an actual class; if 0, it's team generated but not bogus data.
• Any class that is full of seed students should get renamed "seed class " & real_class=0
• For remaining classes, if a class is small, put it into merge table with another class.