Implement NewTerminalUI.
Implement NewFakeUI.
Implement NewTermboxDriver.
Implement NewFakeDriver.
Fix a race condition by initializing FakeUI in constructor.
Initialize App quit channel in New constructor.
Initialize FakeDriver in constructor to fix race condition. Make RuneGrid use Size() instead of Width()/Height() for consistency.
Initialize TerminalUI quit channel in constructor to fix race condition.
Don't close quit channels when services are stopped.