Restrict young users from viewing or posting threads with a certain prefix.

Description
- Makes users below a certain age unable to view threads with a certain prefix, depending on the forum.
 - Makes users below a certain age unable to create threads with a certain prefix, depending on the forum.
 - Age is calculated from birthday options. If these are not set in the user account, a prompt will show up in order to know whether the user wants to change his birthday.

Configuration options:
 - IDs of prefixes that require a certain age. (Comma separated)
 - Forum IDs in which this plugin is active
 - Minimum age to view or post using prefix(es)
 - A few language options