Missing event handlers

[baloola]

Overview

I have noticed that the mouseDown / mouseUp events are missing from the events props, I needed to use them in order to drag specific items.

I noticed it's a bit tricky to use it along with other events, but I think it still might be needed.

I will create a PR in case it is OK to add them :)

Package versions

react-visjs-timeline: 1.5.0
vis version:

Steps to reproduce

Code Snippet

const events = [
  'currentTimeTick',
  'click',
  'contextmenu',
  'doubleClick',
  'groupDragged',
  'changed',
  'rangechange',
  'rangechanged',
  'select',
  'timechange',
  'timechanged',
  'mouseOver',
  'mouseMove',
  'itemover',
  'itemout',
]

Related issues

PR #36 added some missing events ( but not these two )

Screenshots (if appropriate)