message: add h4, h5 and h6
diff: @@ -92,6 +92,9 @@ const BLOCK_TAGS = {
  h1: 'heading-one',
  h2: 'heading-two',
  h3: 'heading-three',
  + h4: 'heading-four,
  + h5: 'heading-five',
  + h6: 'heading-six',
  li: 'list-item',
  ol: 'numbered-list',
  pre: 'code-block',
  @@ -632,6 +635,9 @@ export default class MessageComposerInput extends React.Component {
  this.hasBlock('heading-one') ||
  this.hasBlock('heading-two') ||
  this.hasBlock('heading-three') ||
  + this.hasBlock('heading-four') ||
  + this.hasBlock('heading-five') ||
  + this.hasBlock('heading-six') ||
  this.hasBlock('code-block')))
  {
  return change.setBlocks(DEFAULT_NODE);
  @@ -687,6 +693,9 @@ export default class MessageComposerInput extends React.Component {
  case 'heading-one':
  case 'heading-two':
  case 'heading-three':
  + case 'heading-four':
  + case 'heading-five':
  + case 'heading-six':
  case 'list-item':
  case 'code-block': {
  const isActive = this.hasBlock(type);
  @@ -1215,6 +1224,12 @@ export default class MessageComposerInput extends React.Component {
  return <h2 {...attributes}>{children}</h2>;
  case 'heading-three':
  return <h3 {...attributes}>{children}</h3>;
  + case 'heading-four':
  + return <h4 {...attributes}>{children}</h4>;
  + case 'heading-five':
  + return <h5 {...attributes}>{children}</h5>;
  + case 'heading-six':
  + return <h6 {...attributes}>{children}</h6>;
  case 'list-item':
  return <li {...attributes}>{children}</li>;
  case 'numbered-list':
  