ping.php performance: Cache notification bbcode

- Add two fields to notifiy table to store cached bbcode result
- Add bbcode conversion on notif creation
- Add postfact caching if cache field is empty on retrieval

boot.php

@@ -38,7 +38,7 @@ define ( 'FRIENDICA_PLATFORM',     'Friendica');
 define ( 'FRIENDICA_CODENAME',     'Asparagus');
 define ( 'FRIENDICA_VERSION',      '3.5.1-dev' );
 define ( 'DFRN_PROTOCOL_VERSION',  '2.23'    );
-define ( 'DB_UPDATE_VERSION',      1206      );
+define ( 'DB_UPDATE_VERSION',      1207      );
 
 /**
  * @brief Constant with a HTML line break.