Fixes Bug 1068793 - Mods to signature utilities in prep for Processor2015

in Processor2015, signature generation becomes just another processor rule.  
a rework the .../socorro/processor/signature_utilities.py to create the rule that will be used by Processor2015.

At the same time time, ensure that signature generation compatibility doesn't change for the HybridProcessor.

Also consolidate exist transform rules that deal with signatures into the signature_utilities source file.

oh, yeah, reformatting for style, too. 
shouldn't this be prefixed with `assert `?