Rewritten Image Cache isolation patch for TBB/ESR45
We needed to re-write the Image Cache isolation patch, because the Mozilla introduced a CacheKey that changed how caching works. Fortunately it simplifies our patch somewhat.
Here it is for review: https://github.com/arthuredelstein/tor-browser/commit/1d3f3223629bc37e584fe6592cef83ab01218fce