Refactor ModClusterConfig to allow complex types

mod_cluster's configuration interfaces were originally designed to accept simple configuration property values. With AS7, complex property types (e.g. InetAddress, Collection<InetSocketAddress>, Set<String>) are easier to define - and the old methods are now cumbersome. We should keep the old mutator methods (for backwards compatibility), but alter the accessor methods to accept more complex types.
e.g.
Collection<InetSocketAddress> MCMPConfiguration.getProxies();
void ModClusterConfig.setProxies(Collection<InetSocketAddress>);
void ModClusterConfig.setProxyList(String proxyList);

InetAddress AdvertiseConfiguration.getAdvertiseGroupAddress();
void ModClusterConfig.setProxies(Collection<InetSocketAddress>);
void ModClusterConfig.setProxyList(String proxyList);

etc.