Adding scene table to database setup

Hooked in the scene table, which references the character table.
Modified the message table to reference the scene table instead.
Adding 'choice_selected' field to choice table
Removing uniqueness constraints on database

A temporary measure, until it becomes clear which uniqueness
constraints should be enforced (if any).
Re-organising strings for use in SQL queries
Adding JUnit test class for database

Currently only tests creation of database. Must include I/O
tests, to ensure that database functions as expected.