PMD plugin integration

chore: PMD plugin integration and the respective clean-up

Signed-off-by: Leo Galambos <lg@hq.egothor.org>

build.gradle

@@ -3,6 +3,7 @@ plugins {
     id 'java-library'
     id 'maven-publish'
     id 'com.palantir.git-version' version '4.0.0'
+    id 'pmd'
 }
 
 group 'org.egothor'
@@ -20,6 +21,13 @@ dependencies {
     testRuntimeOnly("org.junit.platform:junit-platform-launcher")
 }
 
+pmd {
+	consoleOutput = true
+	toolVersion = '7.16.0'
+	sourceSets = [sourceSets.main]
+	ruleSetFiles = files(rootProject.file(".ruleset"))
+}
+
 // Apply a specific Java toolchain to ease working on different environments.
 java {
     toolchain {