plugin is incompatible with settings repositories

[jbb01]

When declaring repositories in the dependencyResolutionManagement block in the settings file and setting the repositoryMode to RepositoriesMode.FAIL_ON_PROJECT_REPOS the build will fail with an exception.

An exception occurred applying plugin request [id: 'edu.sc.seis.launch4j', version: '3.0.6']
> Failed to apply plugin 'edu.sc.seis.launch4j'.
   > Build was configured to prefer settings repositories over project repositories but repository 'MavenRepo' was added by plugin 'edu.sc.seis.launch4j'

This seems to be caused by the plugin configuring maven central as the default repository when no project repositories are configured, see

gradle-launch4j/src/main/groovy/edu/sc/seis/launch4j/Launch4jPlugin.groovy

Lines 81 to 84 in 745c0cd

	if (project.repositories.isEmpty()) {
	project.logger.debug("Adding the mavenCentral repository to retrieve the $LAUNCH4J_PLUGIN_NAME files.")
	project.repositories.mavenCentral()
	}

[TheBoegl]

Let's see if we find a solution to this. @jbb01 feel free to create a PR!