Coverage progress bars/colors in report

[skmpowdjy]

What is your use-case and why do you need this feature?
In Jacoco it's super helpful to be able to see the red and green coverage progress bars on the report to quickly tell if something is covered or not.

In Kover, it's much harder to tell due to the numbers getting lost in all the text.

Describe the solution you'd like
A way to display visual progress indicators on the reports (at least the HTML report). Can be optional.

[shanshin]

Relates #272

[shanshin]

This task will be taken into account when migrating to Kotlin Gradle Plugin.

In the future, it will be moved to the Kotlin task tracker, or closed if it loses relevance.