Bug 1030972 - Import tasks from Bugzilla

@bobsilverberg @Osmose r?
This is the result of me adapting `django.views.generic.edit.ProcessFormView` to deal with multiple forms. I noticed that there's a `PUT` in `ProcessFormView`, so I included it in this view too, to be safe.

From the `ProcessFormView` source:
```
    # PUT is a valid HTTP verb for creating (with a known URL) or editing an
    # object, note that browsers only support POST for now.
```