function _initCommandAndKeyMaps() {
        _allCommands = CommandManager.getAll();
        // Keep a copy of the default key bindings before loading user key bindings.
        _defaultKeyMap = _.cloneDeep(_keyMap);
    }
@private

Initializes _allCommands array and _defaultKeyMap so that we can use them for
detecting non-existent commands and restoring the original key binding.