Add column-style-checkbox css variables

[jkusa]

As done with radio buttons, this PR allows column style checkbox icons to be provided by css variables with a native checkbox fallback.

The original material checkbox icons have been moved to the material theme file.

[finos-cla-bot]

Thank you for your contribution and Welcome to our Open Source Community!

To make sure your pull request is accepted successfully, we ask all our open source contributors to sign a Contributor License Agreement; having reviewed our contributor list, we require a CLA for the following people : (@jkusa).

In order to sign a CLA with FINOS, just submit a Pull Request with a simple change to this file (adding an empty line, or some random text at the bottom); this will trigger the EasyCLA bot, which will post a comment to the Pull Request stating whether all PR contributors are covered by FINOS CLA; if not covered, the bot will post instructions on how to sign the CLA.

Thanks once again for your contribution. Let us work with you to make the CLA process quick, easy and efficient so we can move forward with reviewing and accepting your pull request. Feel free to email help@finos.org for any questions.

cc @maoo @TheJuanAndOnly99 @mcleo-d

[jkusa]

CLA signed finos/open-developer-platform#286

[jkusa]

@texodus any update/feedback here?

I've signed the CLA, but the check still shows a failure. Does the check need to be manually retried?

Also, I've found a couple other hardcoded material icons that could be updated to use css vars such as "arrow_back"

I could pick up that change and add a commit to this PR or submit a separate PR if you prefer.

[maoo]

@cla-bot[bot] check

[finos-cla-bot]

The cla-bot has been summoned, and re-checked this pull request!

[maoo]

@texodus any update/feedback here?

I've signed the CLA, but the check still shows a failure. Does the check need to be manually retried?

Also, I've found a couple other hardcoded material icons that could be updated to use css vars such as "arrow_back"

I could pick up that change and add a commit to this PR or submit a separate PR if you prefer.

Hey @jkusa , thanks for your contribution! I've added you to our internal systems, your PR is now validated by our CLA Bot; the same will happen also for your future PRs. Welcome to FINOS!

[jkusa]

Awesome, thanks @maoo!

[texodus]

Thanks for the PR! Looks good!