Feat: Pass validation severity into UI

[anlinguist]

This PR addresses the following discussion and issues:

• custom validator severity #369
• How can I change validation message? #148
• custom validator severity #150

Allows the validation error severity to be warning (yellow), error (red), or info(blue).

If the validation error table is collapsed, it uses the first validation error to determine the color to show.
If the validation error table is opened, each validation error will be the assigned color from the validator.
Also updated the hover color for each validation error.

[josdejong]

Thanks Andrew! I'll review your PR next week.

[josdejong]

Thanks a lot for working out this solution Andrew, this looks good. I made a couple of inline comments. Can you have a look at those?

[josdejong]

Thanks for the updates, this looks really good, both the code and the UI!

[josdejong]

I see there is a linting issue, I'll fix that right after merging.

[josdejong]

After merging I thought it would be neat to rename the helper function getValidationClass to getMaxSeverity, I've changed that in 2c88d93 and 8a6a1de. I hope you don't mind.

[josdejong]

Published now in v0.23.1, thanks again!