rule34.py: Add a list of default filters when searching

When searching with the commands in rule34.py (e.g. ".e621 rating:e winged_unicorn -male -bikini"), add an additional list of filters for the more outlandish or offensive tags (e.g. urine, diaper, blood, etc.). Define the list in a file in Pinkie's config directory and/or load defaults in the rule34 module. 
