Thing: Add __setstate__ method.

Special handling for unpickling is moved out of __getattr__ and
explained better now.
Thing: Delete non-functional _asked_for_data.

Was attempting to check whether Thing._byID had requested data
attributes, but was always set to True by the constructor.
Thing: Remove commented out code.
Thing: Cleanup and simplify __getattr__.
Thing.__getattr__: don't be so careful about getting _essentials.
Thing: replace log_text with g.log.error.
Don't ratelimit comments by users on their own promoted links.
Only put campaigns in underdelivered query if they were charged.
Reset campaign to unauthorized state when its authorization hold expires.