Updated SQL queries to return sqlite3.Row objects.

- Improves overall code readability by replacing indices with keys
- Updated Storage constructor to set DB connection row_factory to
  sqlite3.Row
- Updated Storage.getByID(), Storage.getTop3() and Storage.getQuestion()
  methods to return sqlite3.Row objects
- Affects 'list', 'show', 'accept' and 'rm' commands
- Replaced some if statements with ternary expressions where apprpriate