Initial Setup of Templates for Bootstrap 3 Migrations

might make sense to write this function:
```python
BOOTSTRAP_2 = 'bootstrap-2'
BOOTSTRAP_3 = 'bootstrap-2'
def bootstrap_version(request):
  if hasattr(request, 'preview_bootstrap3') and request.preview_bootstrap3:
    return BOOTSTRAP_3
  return BOOTSTRAP_2
```

and then you can do things like:
```python
template = {
  BOOTSTRAP_2: 'hqwebapp/partials/sidebar.html',
  BOOTSTRAP_3: 'style/includes/navigation_left_sidebar.html',
}[bootstrap_version(request)]
```
(not sure how often this pattern comes up but seems nicer to me)