Fixed race when service manager destructs

Before service with channel could be removed when event-loop is running. It led to bad function call. Now service manager owns all conections to services and it guarantees that all connections will be removed correctly.
Old service client class (service_t) is now renamed in service_connection_t and hidden from user, service manager owns all instances of this class. User access connection through special wrapper (old service_stub_t), that doesn't own connection and throws exception when connection is removed. Since user sees now only service_stub_t, then this class is renamed in service_t.