base PluginError class and auth provider allows overrides
base PluginError class and auth provider allows overrides

Conflicts:
	waterbutler/core/exceptions.py
	waterbutler/server/handlers/core.py

hmoco/waterbutler,Johnetordoff/waterbutler,icereval/waterbutler,RCOSDP/waterbutler,Ghalko/waterbutler,rdhyee/waterbutler,felliott/waterbutler,TomBaxter/waterbutler,cosenal/waterbutler,kwierman/waterbutler,rafaeldelucena/waterbutler,CenterForOpenScience/waterbutler,chrisseto/waterbutler