message: Update PowerSelector to support powerLevelKey prop
  As a key to send as second argument to onChange. This is useful
  when passing the same callback to multiple PowerSelectors.
diff: @@ -42,6 +42,9 @@ module.exports = React.createClass({
  // should the user be able to change the value? false by default.
  disabled: PropTypes.bool,
  onChange: PropTypes.func,
  +
  + // Optional key to pass as the second argument to `onChange`
  + powerLevelKey: PropTypes.string,
  },
  getInitialState: function() {
  @@ -84,17 +87,17 @@ module.exports = React.createClass({
  onSelectChange: function(event) {
  this.setState({ custom: event.target.value === "SELECT_VALUE_CUSTOM" });
  if (event.target.value !== "SELECT_VALUE_CUSTOM") {
  - this.props.onChange(event.target.value);
  + this.props.onChange(event.target.value, this.props.powerLevelKey);
  }
  },
  onCustomBlur: function(event) {
  - this.props.onChange(parseInt(this.refs.custom.value));
  + this.props.onChange(parseInt(this.refs.custom.value), this.props.powerLevelKey);
  },
  onCustomKeyDown: function(event) {
  if (event.key == "Enter") {
  - this.props.onChange(parseInt(this.refs.custom.value));
  + this.props.onChange(parseInt(this.refs.custom.value), this.props.powerLevelKey);
  }
  },
  