Update for release

Update GitHub workflows and CHANGELOG.md

Update IJP Gradle version and fix Key Promoter version number

Merge pull request #125 from halirutan/feat_update_gradle_20

Update build system to IntelliJ Platform Gradle Plugin 2.x

Fix semver version number

Update version with old Gradle plugin

- Although Gradle 2.x plugin does work now, the GitHub actions for testing and publish need to be reworked. Therefore, we use the older Gradle plugin for pushing this update.

Update version

Bump plugin version

Changed improper version entries in CHANGELOG.md to correct format

Add to CHANGELOG.md