Upgrade to Django 1.7.1

This upgrades WACEP to Django 1.7.1. I've gone through some of the courses and it looks like things are working.

The only strange this was that I was getting the error `got an unexpected keyword argument 'related_name'` in the `FigureViewerBlock` model after the upgrade, whenever I ran `manage.py`.

I fixed it by removing the `related_name` argument to `GenericRelation` -- apparently django only wants that argument if it's a `ForeignKey`.

I changed this:
```python
class FigureViewerBlock(models.Model):
    pageblocks = generic.GenericRelation(PageBlock, related_name="FigureViewerBlocks")
```
To this:
```python
class FigureViewerBlock(models.Model):
    pageblocks = generic.GenericRelation(PageBlock)
```

I've also removed a bunch of the lettuce setup stuff -- we're not using that anymore, right?