ADDED: Core - Logger writing log entries to a file.
ADDED: Logging - Timestamps to log output.
ADDED: Logging - Log level to log output.
CHANGED: Core - EntityManager and SystemManager hold references to the game instead of to other managers.
ADDED: Core - Wrapped core game classes by new Infrastructure class.
ADDED: Logging - Writing all game events to log file.
Merge branch 'feature/logging' into develop