Add a preservation_version config to sandbox filters exposing cbuf configs

- update http_status to include 100's (for Loop, but is good in general)
- add a unit test for http_status since it was modified and didn't have one
Clean up unused var
Get rid of the unused HTTP column constants too
Merge pull request #1006 from mozilla-services/filter_preservation

Add a preservation_version config to sandbox filters exposing cbuf configs