No guava dependencies

[pun-ky]

This is an attempt for eliminating Guava related runtime errors like in #190

Improved 2 things:

• removed direct dependency to guava 28-jre which is the even higher version than the most recent version of sonar-java-plugin -26-jre
• removed all Guava usages from code, no imports to classes com.google.*

Regardless Guava version provided by Sonar, our plugin should work fine.

[pun-ky]

as of we are mentioning that most recent version of our plugin requires Java 11, to be able to write code in Java 11 I decided to update it also

[toniedzwiedz]

@pun-ky I've got #196 to build. Once those changes are merged to master and re-integrated into this branch, the build should pass just fine.

[coveralls]

Coverage decreased (-0.5%) to 95.574% when pulling 449927a on no-guava into a4e6d6c on master.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
4 Code Smells

96.0% Coverage
0.0% Duplication

[toniedzwiedz]

Tested the new version with Docker images of SonarQube 7.9.3 and 8.3.0. The exceptions mentioned in #198 and #190 no longer occur. SonarQube starts up successfully.

[toniedzwiedz]

Should also take care of #199