[ticket/12335] Add Events to phpbb\profilefields\manager

These events will allow us to use the raw profile fields data, and process it in other scripts.
My example is this: a user fills in a gaming-character name in a special PF. When the data is retrieved from the database (grab), a script will check to see if the data is valid (custom validation), and retrieve the character information from a remote server and store it in a local database table. In addition, it will automatically be cached in the "$this->profile_cache" by phpBB.

PHPBB3-12335