Demo/move resize items moves timeline when item close to left right border

[davidbejarcaceres]

Issue

Solution for issue #783.
Use the moveResizeValidator() function to move/resize an item close to the left/right border of the timeline, and auto scroll the timeline bounds to the direction of the move/resize item. By doing this you can keep moving/resizing the item without to stop, move timeline and move/resize again and item.

Overview of PR

• Item.js function this.props.moveResizeValidator() will have the same params for move and resize (action, item, time, resizeEdge, event, this.state.dragStart).
• Demo "Move/Resize item close to left/right border, auto scroll timeline" (scrollCloseToBorders) in "demo/app/demo-scroll-close-to-borders/index.js".
• CodeSandbox demo.

Move item left/right
Here you can see the functionality to auto scroll timeline when move item close to left/right borders:

React-Calendar-Timeline.Move.mp4

Resize edges of item left/right
Now for resize item close to left/right borders:

React-Calendar-Timeline.Resize.mp4

Check tests passed
Yes, no errors when running yarn run test, no many changes to library itself, just extra params to the moveResizeValidator function in Iitem.js.