Maven central requirements

According to Maven Central requirements, these are needed:

• JavaDoc (added QDoc in QTTA-91) DONE
• File Checksums (.asc) DONE
• Metadata
  • Correct Coordinates DONE
  • Project Name DONE
  • Description DONE
  • URL DONE
• License Information DONE
  • https://central.sonatype.org/publish/requirements/#license-information 
• Developer Information DONE
  • https://central.sonatype.org/publish/requirements/#developer-information 
• Source control system information DONE
  • https://central.sonatype.org/publish/requirements/#scm-information
• Example .pom file:
  • https://central.sonatype.org/publish/requirements/#a-complete-example-pom
• Signing DONE
  • https://docs.gradle.org/current/userguide/publishing_signing.html#publishing_maven:signing

Because QtGP uses java-gradle-plugin, can't declare these in publications normally in the publication {}:

Workaround: add them in afterEvaluate { publication {}}