Add timestamp to events, update positions on drag, and add `clearOnUnhover` prop.

[Farkites]

About

- [x] Update `elements` property when elements are modified in the Cytoscape UI - [x] Add timestamp to `tapNodeData` and `tapEdgeData` properties such that they trigger a callback on every tap, even if the data itself has not changed - [x] Add timestamp to `mouseoverNodeData` and `mouseoverEdgeData` properties such that they trigger a callback on every mouseover, even if the data itself has not changed - [x] Update documentation - [x] Update tests This PR adds timestamps to some properties so they trigger callbacks every time the cytoscape events happen, adds property `clearOnUnhover` to configure the behaviour of `mouseOver` callbacks, and updates `position` of elements when they are dragged with the mouse. ## Description of changes

Added

• Clear clearOnUnhover property
• Timestamp to tapNodeData and tapEdgeData properties
• Timestamp to mouseoverNodeData and mouseoverEdgeData properties
• Update elements positions when nodes are dragged

Pre-Merge checklist

• [x] The project was correctly built with npm run build:all.
• [x] If there was any conflict, it was solved correctly.
• [x] All changes were documented in CHANGELOG.md.
• [x] All tests on CircleCI have passed.
• [x] All Percy visual changes have been approved.
• [ ] Two people have :dancer:'d the pull request. You can be one of these people if you are a Dash Cytoscape core contributor.

Reference Issues

Closes #[issue number]

Other comments

[emilykl]

@Farkites I just finished a final review over everything except the tests -- looks great!!! 🥇

[emilykl]

@Farkites I was able to run all the Selenium tests locally! I used a different command to run the tests than what's listed in the CONTRIBUTING.md, I'd recommend getting rid of this bit:

Run the following tests:
python -m unittest tests.test_callbacks
python -m unittest tests.test_interactions
python -m unittest tests.test_usage

and replacing it with

Install ChromeDriver following the instructions [here (Mac)](https://www.kenst.com/2015/03/installing-chromedriver-on-mac-osx/) or [here (Windows)](http://jonathansoma.com/lede/foundations-2018/classes/selenium/selenium-windows-install/). You must install the version of ChromeDriver that matches your Chrome version.

Run the tests using the following command:
pytest --headless

[emilykl]

@alexcjohnson @Farkites This looks completely ready to me aside from the lingering Percy test issues... I am approving!

• I see one CI problem where python-3-11 is failing with this error:

  Received a 409 error posting to: https://percy.io/api/v1/builds/30612249/finalize.
  b'{"errors":[{"status":"conflict","detail":"Can only finalize pending builds"}]}'

  It seems like maybe it's failing to finalize because the python-3-11-react-18 has already finalized the build? Do we need to add --nopercyfinalize to one of those commands? Or is there another solution?

• And then there's the question of the failing image tests. Ultimately it seems to me like we should remove a large number of the image tests since most of them are not testing anything useful on the dash-cytoscape level. For now, it seems like the only new issue added by this PR is the timestamp changing in the parameter outputs -- could we deal with that by telling Percy to ignore that image region?