Assignment page not updating after editing a lesson

[chyku]

The assignments page currently refreshes quicker than firebase’s updates after editing a lesson, causing the prior, just-edited lesson’s data to be outdated, corrupting data for the specific case where a teacher edits the same lesson subsequently in the same period.

Possible solutions: set a timeout (not optimal), update firebase dynamically with listeners (listeners + redux, or possibly firebase-react-hooks)

cr @Lam7150