Django 1.7 support for the render functions.

This branch cherry-picks the render files up to 6b9f5da490d1a1b82ff2c2ea66389b243b3d6f37 from project-graphite/graphite-web to get django 1.7 support for views. I chose this route as the files are still on the correct path to HEAD in case we decide to update the entire repo we shouldn't have merge conflicts. I had to apply four patches in order to get the one above to apply cleanly:

```
git cherry-pick -m 6e12f95ea44fba839e5b6b87f6e417d2213bdf26
git cherry-pick -m a225f23a612f9e7b2e6649bdd32ce42d6a262c3c
git cherry-pick -m d9dd40be9dde57bf47a4e9af83b6c913100d26b4
git cherry-pick -m 6b9f5da490d1a1b82ff2c2ea66389b243b3d6f37
```

I tested this against the current ph-graphite stack on 11/10 and it passed smoke tests showing individual image graphs as well as dashboard graphs. I also successfully sent some new metrics from statsgod which displayed properly.

This patch also depends upon a build of graphite-cassandra-plugin at ref: f3e2d89aa61363b64b8e441996be0335269b8049.