MXS-1929: Store filters in smart pointers

The FilterDef structs are now stored in a vector<std::shared_ptr>. This
should make it easier to use filters even if they are deleted before the
session using them closes.

All internal functions now take a smart point as a parameter. One
problematic case will be debugcmd.cc which moves information around as
pointers cast into unsigned longs.

server/core/internal/config_runtime.h

@@ -215,7 +215,7 @@ bool runtime_create_filter(const char *name, const char *module, MXS_CONFIG_PARA
  *
  * @return True if filter was destroyed
  */
-bool runtime_destroy_filter(FilterDef* filter);
+bool runtime_destroy_filter(const SFilterDef& filter);
 
 /**
  * @brief Destroy a monitor
@@ -283,9 +283,9 @@ MXS_MONITOR* runtime_create_monitor_from_json(json_t* json);
  *
  * @param json JSON defining the filter
  *
- * @return Created filter or NULL on error
+ * @return True if filter was created, false on error
  */
-FilterDef* runtime_create_filter_from_json(json_t* json);
+bool runtime_create_filter_from_json(json_t* json);
 
 /**
  * @brief Create a new service from JSON