Add Qulice to police the code quality

[korthout]

Qulice can restrict what kind of code is allowed by breaking the build if the code does not comply.

• Add Qulice to pom file
• Resolve PMD violations
• Resolve Checkstyle violations
• Resolve FindBugs violations
• Make Qulice a standard part of the Travis build

[korthout]

There is an issue with FindBugs that needs to be fixed concerning jdk11. Qulice will break the build because of it. Continue after yegor256/qulice#878 is resolved.

[korthout]

For now it looks like the issue in Qulice will not be fixed soon. Perhaps Findbugs can be disabled completely to at least have a successful build while still be able to use the advantages of checkstyle and pmd via qulice. If so, it might be a good idea to look into applying Spotbugs separately. If not, Qulice can also be replaced by applying Checkstyle and PMD separately, although some checks will be lost. Please investigate.