Refactor Gradle build

[dejan2609]

Note: I already have a pull request for this 😉

Rationale:

• it is always better to use more recent Gradle version
• at the moment it is not possible to use all IDEs (Eclipse, IntelliJ Idea) capabilities; see attached snapshots for more details
  • note: tested with IntelliJ Idea 2020.2.3 and Eclipse 4.17 (Spring Tool Suite 4.8.1)
• also, any gradle command requires explicit project version (or else build fails):

dejan@DESKTOP-Q4CPMFV MINGW64 /c/Work/raccoon4 ((v4.15.0)) $ ./gradlew tasks

FAILURE: Build failed with an exception.

• Where: Build file 'C:\Work\raccoon4\build.gradle' line: 39

• What went wrong: A problem occurred evaluating root project 'Raccoon-desktop'.

  The value of a manifest attribute must not be null (Key=Implementation-Version).

• Try: Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

• Get more help at https:\//help.gradle.org

BUILD FAILED in 824ms

dejan@DESKTOP-Q4CPMFV MINGW64 /c/Work/raccoon4 ((v4.15.0))

[dejan2609]

[dejan2609]

Pull request is merged :tada:, hence closing this issue.