Replaces the old Gradle plugin with plain Gradle buildscripts. Also cleans-up
the current Gradle extensions and re-adds detekt, along with JUnit 5 support to
all modules.
Removes the dependency on legacy script compilation and now relies on script
discovery. In addition, the Gradle build scripts were refactored and updated
to be compatible with Gradle 5.0 and make use of the new java-library
configurations.
Ports the Maven build POMs to Gradle build scripts, which are a bit
friendlier to use. Instead of using the exec:java Maven goal to run the
server now, the gradle run task should be used.