Let plugin initialization fail on unknown configuration fields

[yrucrem]

Currently the object mapper used in PluginConfigUtil#loadConfig()setsDeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIEStofalse`.

Loading the plugin configuration should fail, when the contents of the YAML file does not correspond exactly with the specified class it is deserialized into, to make breaking changes in the configuration more obvious.