The main entrance point for modifying permissions.

• Calls the right function based on the given subaction.
• Checks the permissions, based on the sub-action.
• Called by ?action=managepermissions (1.x) or ?action=admin;area=managepermissions (2.0)
• Loads the ManagePermissions language file.
• Uses the ManagePermissions template file.
• Most sub-actions require the 'manage_permissions' permission
• The 'settings' sub-action (1.1 and 2.0) requires 'admin_forum'