`deletePlugin(id)` which is called by `UpdateManager.uninstallPlugin(id)` failed since the `PluginRepository.deletePluginPath()` call used `Files.deleteIfExists(path)` which is not able to delete recursively. (#135)
Fix bug in load-jars which would not detect jars from lib/ if Path is not absolute
Add slf4j-simple logger in test scope for some logging from tests
Convert some File usage to Path