Jit renderer

This pull request (and branch) is a major overhaul to the architecture of JIT. Instead of a standalone script, JIT is simply another Renderer which inherits all Symphony functionality. This was made possible by Symphony 2.5, which added the `ModifySymphonyLauncher` delegate. This alleviates the major limitation of JIT in that it can now use delegates.

I believe this change would make it possible to fix the following by adding in delegates, or with minor changes to the code:

- Added other modes easily as they can be dropped into `workspace/jit-image-manipulation/filters`, #73
- Adding different cache types, #69
- Allowing image retrieval to come from different sources, #97

The code in this pull request is far from release quality, but I've pushed up in response to [the comment](https://github.com/symphonycms/symphony-2/issues/2266#issuecomment-68440077) by @jensscherbl that others could probably run with this better than I can. Math and image manipulation are not my strengths, so I'm happy for interested parties to carry on this work and work towards a 2.0 release!