Window: View lifecycle, OmicronCLI singleton, getLocalPlayers Optional, Game manual start(), MapView centers.

[FIXED]     Don't trigger enter when InputView is empty.
[ADDED]     Window concept: Windows manage a view lifecycle.
[UPDATED]   OmicronCLI is now a singleton so it's available across threads.
[IMPROVED]  getLocalPlayers is now Optional since there can be no local player; commands adjusted to consider the eventuality.
[IMPROVED]  Game now doesn't start automatically; allow adding GameListeners before starting.
[ADDED]     GameListeners are the new way for UIs to find out about what's happening in the game.
[UPDATED]   MapView now centers on the player's first unit in the map.