message: frontend: add cancel button to YAML editor
diff: import * as React from 'react';
  import { safeLoad, safeDump } from 'js-yaml';
  import { saveAs } from 'file-saver';
  +import { browserHistory } from 'react-router';
  import '../lib/ace/ace';
  import '../lib/ace/mode/mode-yaml';
  @@ -28,6 +29,8 @@ export class EditYAML extends SafetyFirst {
  this.resize_ = () => this.setState({height: this.height});
  // k8s uses strings for resource versions
  this.displayedVersion = '0';
  + // Default cancel action is browser back navigation
  + this.onCancel = 'onCancel' in props ? props.onCancel : browserHistory.goBack;
  }
  handleError(error) {
  @@ -204,6 +207,7 @@ export class EditYAML extends SafetyFirst {
  {create && <button type="submit" className="btn btn-primary" id="save-changes" onClick={() => this.save()}>Create</button>}
  {!create && <button type="submit" className="btn btn-primary" onClick={() => this.save()}>Save Changes</button>}
  {!create && <button type="submit" className="btn btn-default" onClick={() => this.loadYaml(true)}>Reload</button>}
  + <button className="btn btn-default" onClick={() => this.onCancel()}>Cancel</button>
  <button type="submit" className="btn btn-default pull-right" onClick={() => this.download()}><i className="fa fa-download"></i>&nbsp;Download</button>
  </div>
  </div>
  