Gradle build refactoring and version upgrade (5 to 6) :rocket:

[dejan2609]

for rationale see this issue: https://github.com/onyxbits/raccoon4/issues/85

details:

• version upgrades: gradle: 5.6.2 -->> 6.7.1 launch4j plugin: 2.4.3 -->> 2.4.9
• all gradle plugins are moved under 'plugins' section (legacy 'apply' directive is removed)
• project version is moved to a 'gradle.properties' file (rationale: now IDEs are able to import project without warnings/errors)
• gradle wrapper section introduced with gradle distribution switched from 'bin' to 'all' (useful for IDEs, among other things)
• .gitignore file: IntelliJ Idea entry is added
• deprecated gradle properties are replaced: 'version' -->> 'archiveVersion' 'baseName' -->> 'archiveBaseName'

related links:

• https://docs.gradle.org/current/userguide/upgrading_version_5.html#changes_for_archive_tasks_zip_jar_war_ear_tar
• https://docs.gradle.org/6.7.1/dsl/org.gradle.api.tasks.bundling.AbstractArchiveTask.html#org.gradle.api.tasks.bundling.AbstractArchiveTask:version
• https://docs.gradle.org/6.7.1/dsl/org.gradle.api.tasks.bundling.AbstractArchiveTask.html#org.gradle.api.tasks.bundling.AbstractArchiveTask:baseName

[dejan2609]

Small change: I'm going to force-push in order to solve GitHub warning No new line at the end of file

[dejan2609]

@onyxbits please review this PR (small note: I will also upgrade your build for Gradle 7.x version at some point).

[dejan2609]

@onyxbits can you please review this ?

[onyxbits]

Hi, sorry. Been incredibly busy the past few weeks, so I lost sight of this.

[dejan2609]

No worries @onyxbits ! Thanks for investing your time to review and merge this.