Overhaul configuration: make log location customisable.

- Change Configuration to singleton class from module.
- Remove #detect_debug_mode, #detect_trace_mode and VEDEU_ environment variables.
- Rename #system_key_options to #system_keys.
- Set default log to /tmp/vedeu.log.
- Add ability to reset configuration.
- Add configuration to test_helper; will write to 'vedeu_test_helper.log'.
- Add missing require statements.
- Add more documentation.
- Add more tests and tidy up tests.
- Remove MonoLogger.
- Update example apps to use new configuration DSL.
- Fix path and add quit key information.
- Use custom log file path if provided.
- Add configuration option for log filepath.
- Suppress test colour output via environment variable.
- Add .reset! to remove all entities from all repositories.