MXS-2304 Add ctor/dtor and other functions to parameter class

The manipulation functions are currently static so that the container can be initialized
if required. This will be fixed later.

The new functions are taken into use in monitor management.

server/core/config_runtime.cc

@@ -583,8 +583,7 @@ bool do_alter_monitor(Monitor* monitor, const char* key, const char* value)
     }
 
     std::lock_guard<std::mutex> guard(crt_lock);
-
-    monitor_set_parameter(monitor, key, value);
+    MXS_CONFIG_PARAMETER::set(&monitor->parameters, key, value);
     bool success = true;
     if (strcmp(key, CN_USER) == 0)
     {