Access control

Merged in the AccessControl work I did refactoring and adding logging.  Originally these were in CoreAccessControl and AdminUIAccessControl classes, but it was suggested I should merge it all in rather than maintaining separate classes.  This also rearranges the inheritance a little so BaseAccessControl has the effect of NullAccessControl and all classes add to and override functions from Base to extend functionality.
Is there a test for aff4:////C.123123123? we should probably add some like this...