Add shouldIgnoreURI pre-rewrite filter for URI's

Don't try to rewrite OCSP requests or URI's whose scheme is
something other than "http" or "https" (ex: "about:newtab").
Add common OCSP responder list from SSL Obs. data
Ignore OCSP (Firefox 32+)

Currently we have two solutions to this; now let's merge them...
Merge the two OCSP-avoidance approaches

One for FF 32+, one for <32
Remove dangling call to old code
Fix plumbing
Merge pull request #332 from EFForg/fix/ocsp

Add filter for requests that we shouldn't try to rewrite. (in progress)