Allow custom authenticator to be added via configuration

Introduce new configuration parameter (authenticatorClass) that is used to specify custom authenticator class. This authenticator class will be found, instance will be created (if class has a constructor that takes Configuration as parameter, jolokia runtime configuration will be provided, allowing authenticator to take it into account). Newly created instance of authenticator will be set for Jolokia server to use. If authenticatorClass config parameter was not provided, code will fall back to old logic (i.e. check if user/password is set and create default authenticator).

This pull request also adds a ugly looking code into copyResourceToTemp method of JvmAgentConfigTest with the main goal of properly escaping paths used in tests when they are run win (tested on win7).