Clientside prevent update

[jjaraalm]

Adds dash_clientside.no_update and dash_clientside.PreventUpdate to fix #963. Integration tests added and passing.

Also changed a Popen call in _utils.py so that the path is properly searched on windows machines. Otherwise, building was failing for me. Feel free to remove if you think it's not necessary.

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • Allow clientside updates to be prevented.
• I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• I have added entry in the CHANGELOG.md
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follow
  • this github #PR number updates the dash docs
  • here is the show and tell thread in plotly dash community

[alexcjohnson]

Thanks @jjaraalm - looks fantastic. Very nice tests, very clean implementation.

To get the linter to pass, just cd dash-renderer then npm run format. We use prettier, which is sufficiently opinionated that I don't even know how to write compliant code myself, I just have it reformat whatever I write.

[jjaraalm]

Thanks! It's all good, one day I hope to make my linters happy without effort ... one day ... maybe

[alexcjohnson]

Alright, looks great! This definitely merits an entry in the changelog, then it'll be ready to go. We'll hold off merging for a couple of days though, as we're planning a patch release 1.4.1 and this has new features so needs to go in a minor (1.5.0)

[chriddyp]

This is great 🎉
Congrats @jjaraalm on braving your way through dash-renderer/src/actions/index.js . You are one of the first community contributors to do so! 🏆 🏆 🏆

[jjaraalm]

Thanks @chriddyp !

@alexcjohnson should I update the changelog or will you all do it?

[alexcjohnson]

@jjaraalm go for it! Just add

## Unreleased
### Added

at the top, and try to format the entry like the ones below it.

[alexcjohnson]

FYI @rpkyle - I think this namespace exclusion is the only piece of this PR that's relevant to R

[alexcjohnson]

💃 Beautiful, very nicely done!