I believe the ARDrone_Developer_Guide.pdf (in the SDK 2.0) to be pretty complete. Or, given that the SDK 2.0 is now unsupported, it's as good and as complete as it's going to get!
Yes, there are more
AT* commands in the code (e.g.
at_msgs.h) than listed in the developer guide, but I figure these are unsupported commands and either of no interest to the casual developer, or there's a better way to perform the same task.
For example, the undocumented
AT*LED command has been superseded with the
leds:leds_anim config - which is arguably better because the drone acknowledges config commands.
As for task and task activation models, I'm afraid I've no idea what they are. Your best bet is to search through the SDK code.