Convert avrorouter objects to C++

The instance and session objects are now C++ structs. The next pointers
for the sessions was removed as it is not the appropriate place to store
this information. This means that the client notification functionality is
broken in this commit.

server/modules/routing/avrorouter/avro_schema.cc

@@ -15,7 +15,7 @@
  * @file avro_schema.c - Avro schema related functions
  */
 
-#include "avrorouter.h"
+#include "avrorouter.hh"
 
 #include <maxscale/mysql_utils.h>
 #include <jansson.h>
@@ -972,7 +972,7 @@ static bool extract_create_like_identifier(const char* sql, size_t len, char* ta
 /**
  * Create a table from another table
  */
-TABLE_CREATE* table_create_copy(AVRO_INSTANCE *router, const char* sql, size_t len, const char* db)
+TABLE_CREATE* table_create_copy(Avro *router, const char* sql, size_t len, const char* db)
 {
     TABLE_CREATE* rval = NULL;
     char target[MYSQL_TABLE_MAXLEN + 1] = "";