feat: row direction support (#337)

* css direction change

* direction attribute added to test snapshot

* direction attr set to 'ltr' by default, ltr classes added

* updating tests and cleaning up

* removing rtl from demo

* prettier

* default rowDirection=ltr

* update props

* documentation

* updating snapshot

Author: wuweiweiwu

Diff for: README.md

@@ -93,6 +93,7 @@ export default class Tree extends Component {
 | onVisibilityToggle             |      func      | Called after children nodes collapsed or expanded. <div>`({ treeData: object[], node: object, expanded: bool, path: number[] or string[] }): void`</div>                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
 | onDragStateChanged             |      func      | Called when a drag is initiated or ended. <div>`({ isDragging: bool, draggedNode: object }): void`</div>                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
 | maxDepth                       |     number     | Maximum depth nodes can be inserted at. Defaults to infinite.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
+| rowDirection                   |     string     | Adds row direction support if set to `'rtl'` Defaults to `'ltr'`.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
 | canDrag                        |  func or bool  | Return false from callback to prevent node from dragging, by hiding the drag handle. Set prop to `false` to disable dragging on all nodes. Defaults to `true`. <div>`({ node: object, path: number[] or string[], treeIndex: number, lowerSiblingCounts: number[], isSearchMatch: bool, isSearchFocus: bool }): bool`</div>                                                                                                                                                                                                                                                                                                                        |
 | canDrop                        |      func      | Return false to prevent node from dropping in the given location. <div>`({ node: object, prevPath: number[] or string[], prevParent: object, prevTreeIndex: number, nextPath: number[] or string[], nextParent: object, nextTreeIndex: number }): bool`</div>                                                                                                                                                                                                                                                                                                                                                                                      |
 | theme                          |     object     | Set an all-in-one packaged appearance for the tree. See the [Themes](#themes) section for more information.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |