Use waffle Switch homepage_2015

I  reverted the original view to the version in the current master, then implemented a new view and associated helper functions to use a waffle Switch, as we discussed earlier.

To test this locally, when you first load the homepage you should see exactly what's in current master.
To see the new homepage:
`./manage.py shell_plus`
```python
Switch.objects.create(name='homepage_2015', active=True)
```
Then restart your dev server to flush LocMemCache (or flush memcached if you're using it), and you should see the new homepage.
Do we still need this lang file tag?