Back end: Implemented the message queue. Resolves #113.
Merge branch 'master' of https://github.com/L6mps/LasaLaraAP into Backend
Merge remote-tracking branch 'origin/master' into Backend
Back end: Fixed SQL WHERE clauses. #75, #108.
Back end: Fixed progress calculation when there are no books. Resolves #117.
Back end: Refactored data preloading. #75, resolves #35, resolves #40, resolves #79.
Front end: Updated progress queries.