Use compile dependency to Kover Features in Kover Gradle Plugin

[shanshin]

Since the version of the aggregator and report generator has been enshrined in the Kover Gradle Plugin for a long time, it makes no sense to use dynamic classpath of and classloader isolations in Gradle Workers.

We can use Kover Features as a compile dependency and use its API.

Steps

• extract all functions to generate reports (including validation) to Kover Features artifact, create own unified api for this
• add compile dependency on Kover Features
• replace all calls of intellij-reporter with calls to Kover Features
• remove the use of Gradle Workers
• remove all intellij dependencies from Kover Gradle Plugin

This change can also eliminate the error with access to Freemarker template inside Gradle Worker, and simplify the implementation of warn on verification error.

[shanshin]

Implemented in 0.8.0-Beta2