minor cleanups and code deduplication

Hi,
 
while browsing the veewee sources I noticed that the debug option is set as method_option 
on nearly every (task) method. I made this a class_option instead to make it available for
every (even new) task methods in the class and to remove some duplicated code.
It would be nice if you can include this into your master.

Cheers,
Ruben