Rename MODULE_INFO to MXS_MODULE

The MODULE_INFO is now the main object which is used by modules to convey
information to the MaxScale core. The MXS_MODULE name is more apt as it
now contains the actual module definition.

The old MODULES structure was moved into load_utils.c as an internal
implementation and was renamed so that it is not confused with the new
MODULE structure.

include/maxscale/filter.hh

@@ -193,7 +193,7 @@ protected:
  * The plugin function @c GetModuleObject is then implemented as follows:
  *
  * @code
- * extern "C" MODULE_INFO* MXS_CREATE_MODULE()
+ * extern "C" MODULE* MXS_CREATE_MODULE()
  * {
  *     return &MyFilter::s_object;
  * };