Add state samples.
Merge required changes from dev.
Add method UIImpl::poll_event.
Add UI field into StateManager.
Add event handling in main menu.
Fix game state.
Add state StartGame.
Pass UI into IState::draw.
Add game stuff into GameState.
Move state sources into src/state dir.
Fix indentation.
Merge PlayerFactory fix.
Fix state name typo.
Add default player set in GameStart.
Fix state switching in main menu.
Fix var name in GameState::handle_events.
Merge 'feature-add-menu'.
Add menu into start game state.
Merge menu bugfixing.
Add Window interface.