Back end: Refactored getting all of the questions in a chapter. Resolves #129.
Back end: Refactored exception handling (still have a long way to go). #52, #114.
Back end: Refactored data downloading stages. Resolves #121.
Back end: Started refactoring book updating functionality. #41, #75, #77.
Back end: Implemented book updating functionality. #41, resolves #75, resolves #77.
Back end: Implemented question posing functionality. #41, resolves #30.
Back end: Refactored database insertion on book updating. #41, resolves #130.
Android app install location to prefer external storage. Resolves #54.
Back end: Implemented page view switching functionality. The changing of the known date of questions was not necessary. Resolves #107.
Back end: Implemented book and chapter completeness checking. Resolves #132.
Back end: Removed unnecessary variables on database usage. Resolves #109.
Back end: Fixed null pointer exception in book chapter list.
Merge branch 'Backend'